US President Donald Trump used his first full day in office to wage war on the media, accusing news organisations of lying about the size of his inauguration crowd as huge protests served notice that a vocal and resolute opposition would be a hallmark of his presidency.

Americans took to the streets in red and blue states alike to emphatically decry a president they consider reprehensible and, even, illegitimate. Trump visited the Central Intelligence Agency for a stream-of-consciousness airing of grievances -- including against journalists, whom he called "the most dishonest human beings on Earth".

Shortly afterwards, press secretary Sean Spicer addressed the media for the first time from the White House, where he yelled at the assembled press corps and charged it with "sowing division" with "deliberately false reporting" of Trump's inauguration crowd.

At the White House, where the chants of a huge crowd on the Mall for the Women's March on Washington could be heard for much of the day, Trump's advisers grappled with this difficult reality: There will be no honeymoon for the 45th president.


President Barack Obama, had urged Americans to give his successor a chance. But the activists who stirred the masses vowed to obstruct Trump's agenda on such issues as healthcare, climate change, criminal justice, gay rights and access to abortion and birth control.

"This is likely to be a feature of the entire presidency," said Steve Schmidt, a veteran Republican strategist who criticised Trump's candidacy.

"If you look back to the rise of the Tea Party over 2009 and 2010 -- the revolt that took place at the town hall meetings, the protests -- that's starting with this president at an earlier hour and in numbers that are by orders of magnitude greater."

David Axelrod, one of Obama's closest advisers and an architect of his campaign strategies, said it is incumbent upon Trump's opponents to do more than march. "This is an impressive display today. But if it isn't channelled into organising in a focused way, then it is cathartic but not in the long run meaningful. That's the challenge for the progressive community."

The Women's March protests kicked off in New Zealand and Australia on Saturday.

Trump spent yesterday concentrated on the day before -- claiming that the crowd for his swearing-in stretched down the Mall to the Washington Monument.

It did not.

Protesters walk on Independence Avenue during the Women's March on Washington. Photo / AP
Protesters walk on Independence Avenue during the Women's March on Washington. Photo / AP

Trump accused television networks of showing "an empty field" and reporting that he drew just 250,000 people to witness Saturday's ceremony.

"It looked like a million, a million and a half people," Trump said.

"It's a lie. We caught [the media]. We caught them in a beauty."

During his 2009 inaugural address, President Barack Obama's crowd extended that far, and a side-by-side comparison of aerial photos from both inaugurations clearly shows that Obama's crowd was much larger than Trump's.

Spicer echoed his boss's assertion about the inauguration, insisting from behind the podium at the White House press briefing room that more than 700,000 people stretched down the Mall to the Washington Monument.

"This was the largest audience to ever witness an inauguration, period -- both in person and around the globe," Spicer said, less than a minute after declaring that "no one had numbers" because the National Park Service, which controls the Mall, does not release crowd estimates.

One verifiable number that Spicer offered was that ridership on Washington's subway system was higher than for Obama's inauguration four years ago. Spicer said that 420,000 people rode Metro on Saturday, while only 317,000 did so for Obama in 2013.

Both of these numbers are inaccurate.

Nearly 571,000 people rode on Saturday, and 782,000 rode on Inauguration Day four years ago, according to the Washington Metropolitan Area Transit Authority.

Spicer warned journalists that they are in for more sparring with the new administration.

"There's been a lot of talk in the media about the responsibility to hold Donald Trump accountable, and I'm here to tell you that it goes two ways," he said.

"We're going to hold the press accountable as well."

In a highly unusual move, Spicer left the briefing room without answering questions from reporters, including one shouted at him about the Women's March on Washington.

Protesters rally against President Donald Trump during a women's march. Photo / AP
Protesters rally against President Donald Trump during a women's march. Photo / AP

Trump and Spicer also lambasted a member of the White House press pool who reported that Trump had removed a bust of civil rights icon the Rev Martin Luther King jnr from the Oval Office. The bust remains in the Oval Office, but pool reporter Zeke Miller of Time magazine did not see it during a brief visit to witness Trump signing an executive order on health care. Miller corrected his pool report and tweet and publicly apologised for the mistake. In response, Spicer tweeted, "Apology accepted."

Nonetheless, Trump called the episode an example of "how dishonest the media is".

Trump visited the CIA's headquarters in Langley, Virginia, to express his gratitude for the intelligence community, which he had repeatedly railed against during the transition period and recently likened to Nazis.

What Trump delivered before some 400 career intelligence officers was a disjointed, campaign-style monologue. He complained about the Senate delaying confirmation of his nominees; critics questioning whether he is smart and vigorous; and journalists reporting on the size of his inauguration crowd. "I have a running war with the media. They are among the most dishonest human beings on Earth, right?"

Many in the crowd -- which was composed of agency employees who had signed up to see him speak as well as some of Trump's White House aides -- applauded. At one point, Trump claimed that most of the people in the room had voted for him.

In his remarks at Langley, Trump vowed to lead the fight against Isis (Islamic State): "We have not used the real abilities that we have."

Trump also delved into the Iraq War, repeating his oft-stated belief that the United States bungled its exit from the country by not taking Iraq's oil, which he said was how Isis made its money. "The old expression, to the victor belong the spoils," he said, adding: "We should've kept the oil. But, OK, maybe we'll have another chance."