Obama, who established his political career in Chicago, was spending election night in the Windy City - but elsewhere around the country supporters of his Republican challenger Mitt Romney were equally confident of victory.
"We need to change this president," said Ruben Salazar, 72, a Cuban-American who got up early to cast his ballot in Miami. "I need a job for my wife, for my daughter, a better future for my grandsons. That's why I'll vote for Romney."
The United States has no central election authority, but with several hours to go before polls close, state and local officials tasked with electoral logistics reported a strong turnout.
So did an unaffiliated group supporting Romney's vice-presidential running mate Paul Ryan - "The Campaign to Defeat Obama" - in a fundraising email.
"Polling location analysis indicates there is heavy Democrat turnout so far today," it said in a fundraising email. "We have to counteract this with a late surge of Republican and conservative Independent turnout."
Florida's secretary of state Ken Detzner said turnout in his state - one of the so-called "battlegrounds" where the local results could swing the national outcome - could be "record-setting" this year.
"We're excited on both sides," said Caitrin McCarron, a Republican supporter in Arlington, Virginia, across the Potomac River from Washington, where lines began forming at polling stations before the crack of dawn.
"Virginia is obviously a battleground state," she told AFP, using the American political lingo for a hotly-contested state where the result could swing the final national outcome.
In New Jersey, reeling from superstorm Sandy which left thousands suddenly homeless last week, large numbers of voters waited in line impatiently amid rubble and rotting rubbish.
In Hoboken, across the Hudson River from New York City, one makeshift polling station was 40 minutes late in opening, drawing complaints from the 60 or so people in line.
"Please excuse the appearance of this place," a poll worker told the crowd. "Two days ago, it was under two feet of water."
Voters in the battleground state of Ohio wrestled with unusually long ballot papers due to the fact that they were voting not only for the next US president, but also for changes to the state constitution.
"I think that if you had not done some homework, it was very confusing," said Annie Hamilton, a Democrat in University Heights, outside Cleveland.
In southern California, a mariachi band walked the streets of Van Nuys early in the day, stirring up the Latino vote for Obama with popular tunes like "La Bikina". Trailing them was a banner that read: "For our American Dream."
In Oakland, across the bay from famously liberal San Francisco, Tommy Jones, 56, waited 10 minutes to vote at a Baptist church, only to find the line twice as long when he exited.
"As a black man, it is as important to vote this time as any time," said Jones as a woman stepped out of the church, pumped her fist and softly chanted: "Obama."
Online, many Americans used Twitter to post photos of themselves voting, and FourSquare to pinpoint where they did so. Google re-doodled its homepage logo to help users locate their nearest polling station.
Some went so far as to post Instagrams of their ballot papers - something that, in some states, could be deemed illegal.
Tuesday's very first ballots were cast just after midnight in the New Hampshire hamlet of Dixville Notch, where they were immediately counted. For the first time ever, it was a tie: five for Obama, five for Romney.
OBAMA PLAYS SOME BASKETBALL
US President Barack Obama burned off his election-day nerves in traditional fashion, with a game of basketball with close friends, as millions of Americans went to the polls.
Obama gathered an all-star line-up including Chicago Bulls great Scottie Pippen, his brother-in-law Craig Robinson, who is a college basketball coach, White House chef Sam Kass and Education Secretary Arne Duncan.
The president started his election day tradition during his 2008 primary run against Democratic foe Hillary Clinton, as a way to burn off the long hours between the end of the campaign and the counting of votes.
Alexi Giannoulias, a former Illinois state treasurer who also played in the game, said two five-player teams played four 12-minute quarters in the game, and swapped out periodically with substitutes.
He said the president, who is known to be a competitive player who trash talks teammates and opponents alike, led his team to victory, though wouldn't say how many points Obama posted.
After the game, in an athletic centre near the president's Kenwood neighborhood in Chicago, Obama returned to his house, where he was to eat dinner with his family and wait for the results to pour in.
He and his wife Michelle were due to be joined by their daughters, Malia, 14 and Sasha, 11, for election night events, after they finished their school day at the private Sidwell Friends school in Washington.
LAWSUITS, FIGHTS, DELAYS AS VOTING BEGINS
Sporadic problems have been reported at polling places around the US, including a confrontation in Pennsylvania involving Republican inspectors over access to some polls and a last-minute court fight in Ohio over election software.
One Florida elections office mistakenly told voters in robocalls the election was the following day.
Although the majority of complaints were simply long lines, the Election Protection coalition of civil rights and voting access groups said they had gotten some more serious calls among more than 35,000 received on a toll-free voter protection hotline.
""It's already started and it's busy," said Barbara Arnwine, president of the Lawyers Committee for Civil Rights Under Law.
In Philadelphia, the Republican Party said 75 legally credentialed voting inspectors were removed from polling places in the heavily Democratic city, prompting the GOP to seek a court order providing them access.
Local prosecutors were also looking into the reports. Democratic Party officials did not immediately return a message seeking comment.
The battleground state of Ohio was the scene of yet another court battle, this one involving a lawsuit claiming voting software installed by the state could allow manipulation of ballots by non-election board officials.
The lawsuit wants a judge to order Ohio not to use the software - something state elections officials said would "unnecessarily thwart the smooth operation of the election".
The Florida robocall glitch occurred in Pinellas County, location of St Petersburg and Tampa Bay. Officials said the calls intended for Monday were wrongly recycled Tuesday, telling possibly thousands of voters they had until "7pm tomorrow" to vote, according to the Tampa Bay Times.
Nancy Whitlock, spokeswoman for the county's supervisor of elections, said officials immediately stopped the calls Tuesday morning when the problem was discovered and a second message went out telling voters to disregard the previous call.
Elsewhere, the Election Protection coalition reported problems with ballot scanners in the Ohio cities of Cleveland, Dayton and Toledo; late-opening polling places in minority neighborhoods in Galveston, Texas; and some precincts in the Tampa, Fla., area where voters are being redirected to another polling place where they must cast a provisional ballot.
Meanwhile, voters in several storm-ravaged areas in New York and New Jersey expressed relief and even elation at being able to vote at all, considering the devastation from Superstorm Sandy. Lines were long in Point Pleasant, NJ, where residents from the Jersey Shore communities of Point Pleasant Beach and Mantoloking had to cast their ballots due to damage in their hometowns. Many people still have no power eight days after Sandy pummeled the shore.
"Nothing is more important than voting. What is the connection between voting and this?" said Alex Shamis, a resident of hard-hit Staten Island, gesturing to his mud-filled home.
Any voting problems are being closely monitored after months of legal and political battles over more voter ID restrictions and other laws, mostly fruitless hunts for supposedly ineligible people on voting rolls in many states and sustained claims that black and Hispanic voters are being targeted for intimidation and suppression.
Michael Waldman, president of the Brennan Center for Justice at New York University, said even in states where the restrictive laws have been blocked or delayed, many people still think they are in effect.
"The laws were struck down but the confusion remains," Waldman said.
Many of these issues could resurface in the courts after Tuesday, particularly if the race between President Barack Obama and his Republican challenger, Mitt Romney, is too close to call or heads for a recount in states such as Ohio or Florida.
The Justice Department will have at least 780 observers at key polling places in 23 states to ensure compliance with the 1965 Voting Rights Act and look into any allegations of voter fraud.
Provisional ballots were the latest legal skirmish in the critical battleground state of Ohio, where Secretary of State Jon Husted's decision on how they can be cast was challenged in federal court.
Advocates and lawyers for labor unions contend Husted's order would lead to some provisional ballots being rejected improperly because the burden of recording the form of ID used on a provisional ballot is being placed on voters, not poll workers as in the past.
A provisional vote allows a person to have his or her say, but the ballot is subject to review and verification of eligibility.
A decision was not expected before Election Day, but the judge overseeing the case planned a ruling before November 17, when provisional ballots can begin to be counted in Ohio. Provisional ballots are used more often in Ohio than in most states, with experts predicting between 200,000 and 300,000 will be cast there.
"That could be a huge problem after Election Day for counting ballots," said Wendy Weiser, director of the Brennan Center's Democracy Program. "There's really tens of thousands of voters in Ohio whose votes could be at risk."
PATIENT VOTERS MAKE THEIR DECISION
From storm-ravaged New Jersey to a sun-kissed California, millions of Americans have lined up to vote in the dramatic climax of a hard-fought race between Barack Obama and Mitt Romney.
Many were patient. Some were jittery. Still others - especially those enduring power outages and the mountains of debris left by superstorm Sandy last week - were understandably a bit cranky.
For many, a palpable sense of excitement hung over what they saw as a crossroads for deeply divided and economically struggling America, with citizens choosing between two men with very different visions.
"It's very exciting, I love the turnout," said Cal Alde of Falls Church, Virginia, outside Washington, who sported a festive star-spangled top hat and a "Keep Obama and carry on" T-shirt after casting his vote.
"But we're biased," added his colleague Will Farnam, wearing a pro-Obama badge while breakfasting on a bagel at Starbucks. "There are a lot of Romney people out there ... It's going to be tight."
"We're excited on both sides," said Caitrin McCarron, a Republican supporter in nearby Arlington, Virginia.
"Virginia is obviously a battleground state," she said, using the American political lingo for a hotly-contested state where the result could swing the final national outcome.
"Everyone is coming out and excited and hopefully, by the end of the night, we'll know who is going to be our next president.''
In New Jersey, reeling from superstorm Sandy which left thousands suddenly homeless last week, voters waited in line impatiently amid rubble and rotting rubbish.
In Hoboken, across the Hudson River from New York City, one makeshift polling station was 40 minutes late in opening, drawing complaints from the 60 or so people in line.
"Please excuse the appearance of this place," a poll worker told the crowd. "Two days ago, it was under two feet of water."
By mid-day, the waiting time at one polling station in Fairfax County outside Washington was three hours, a reporter said.
Voters in the battleground state of Ohio were wrestling with unusually long ballot papers due to the fact that they were voting not only for the next US president, but also for changes to the state constitution.
"I think that if you had not done some homework, it was very confusing," said Annie Hamilton, a Democrat in University Heights, outside Cleveland.
In Chicago, on the other hand, few voters were seen when polls opened at dawn - possibly a reflection of how many, like president Obama himself, took advantage of early voting opportunities.
By some estimates, more than a third of Americans voted early - something the Obama campaign actively encouraged.
In another battleground state, Florida, which decided the 2000 election for George W Bush, long lines formed early at polling stations as weather forecasters warned of thunderstorms later in the day.
First-time voter Mary Ann Weber, 20, a University of Miami architecture student, turned up four hours early to be among the first to weigh in. She said she backed Obama, seeing him as a force for social change.
But another early-riser, Cuban-American Ruben Salazar, 72, favored Romney: "We need to change this president. I need a job for my wife, for my daughter, a better future for my grandsons, and that's why I'll vote for Romney."
In southern California, a mariachi band walked the streets of Van Nuys early in the day, stirring up the Latino vote for Obama with popular tunes like La Bikina.
Behind them was a banner that read: "For our American Dream."
In Oakland, across the bay from unabashedly liberal San Francisco, Tommy Jones, 56, waited 10 minutes to vote at a Baptist church, only to find the line twice as long when he exited.
"As a black man it is as important to vote this time as any time," he said, as a woman stepped out of the church, pumped her fist and softly chanted: "Obama."
Online, many Americans used Twitter to post photos of themselves voting, and FourSquare to pinpoint where they did so. Google re-doodled its homepage logo to help users locate their nearest polling station.
''#iVoted for #TeamObama. Had to put an extra check for good measure!,'' New York tweeter @Stwo said, attaching a photo of his ballot paper which bore the names of candidates in English and Chinese.
OBAMA HAS WHIFF OF VICTORY
President Barack Obama danced on the stage wrapping up a rally in Cincinnati, Ohio.
Yesterday - his last rally as an election candidate - he bounded forth with a wide grin before a crowd in Madison, Wisconsin, energised by ballads from Bruce Springsteen.
Did the whiff of victory hang here in the cold, blue-sky air?
The fate and the legacy of Obama, the bruised Messiah for hope and change, are now in the hands of the American people who will pour into polling stations today. Complacency remains a luxury unavailable to him; yet the runes seem clear, something was nudging his way.
For one more gruelling day of rallies across four swing states the task for Obama was to cajole supporters to turn out and to detail the case for himself and against Mitt Romney.
"Our work is not yet done," he said here, saying the nation faced a historic choice between two distinct visions.
"It's a choice between returning to the top-down policies that crashed our economy or a future that provides opportunities for everybody."
Some national polls still showed a tie. The final national NBC/Wall Street Journal survey had Obama with the support of 48 per cent of likely voters and Romney securing 47 per cent. But the polls that mattered - in Wisconsin and the other eight battleground states - showed the avenues to the 270 Electoral College votes needed to win looked more numerous and more wide for the incumbent.
It would seem Obama has held on to his edge, or even built on it, in the Midwest, notably in Ohio, but also in Wisconsin and Iowa. Moreover, he had built an advantage in early voting patterns. Upwards of 30 million Americans had voted in 34 states and the District of Columbia by last night. Those early votes have established leads for the President in Nevada, Iowa and Ohio, even if not by the margins of 2008.
"Here's what I predict, it will not be tied tomorrow," David Axelrod, the Obama strategist, boldly told a huddle of reporters, asserting that "all those pathways" to a College victory he had laid out one year ago, "are intact".
"We feel good here in Wisconsin where we have a solid lead and have the enthusiasm. We are going to have a good day in Ohio and we are going to have a good day in Iowa." In Florida, Obama is "competitive", he said only.
Pundits are naturally shy of iron-clad predictions. Those reporters who were in Crawford, Texas, in 2004 remember a downcast George W. Bush registering his vote with models showing a very slim lead that election day for the Democrat, John Kerry. Bush instead won a second term.
The Associated Press offered its final analysis. Obama was almost assured 249 Electoral College votes by carrying 20 states that are reliably Democratic or leaning his way, and the District of Columbia. Romney could count on just 206 from 24 states that are strong Republican territory or lean right. The distance that must be made up in the battleground states to the magic 270-mark is thus far greater for one than the other.
"It's going to be great to feel the power of your votes and voices tomorrow," Springsteen told 18,000 supporters before launching into his vocal and mouth organ melody Promised Land.
Nothing has bothered Obama more than Romney trying to usurp the "change" mantle he claimed for himself in 2008. On the trail he has flattered Romney with faint mockery as merely a salesman.
"We know what change looks like, Madison, and what he's selling isn't it ... I know what real change looks like ... because I have fought for it, you see the scars I have earned for it and you have seen the grey hairs on my head."
Some in Team Obama, which saw the President yesterday hold one final rally in Des Moines, Iowa, the state that launched his Hope and Change dream in the caucuses of 2008, didn't want to jinx what they were daring to spy. Superstition is hard to shake and some among them were refusing to shave until the votes were all in. But one other bristly consigliore of the President said: "We feel good, we feel good."
What song was Obama jiving to in Ohio? "Signed, Sealed, Delivered". Maybe Mr President. But not quite yet.
ROMNEY CASTS HIS VOTE
White House hopeful Mitt Romney and his wife, Ann, have voted in the US election.
The Romneys voted in the town of Belmont, Massachusetts.
The Republican nominee then headed to Ohio and Pennsylvania for last-minute efforts there.
Asked who he voted for, Romney said: "I think you know,'' adding he felt "very, very good" about his election prospects.
- Independent, AFP, AP
