US President Barack Obama briefly addressed the FBI's reopened investigation into Hillary Clinton's email practices for the first time, saying in an interview that the agency does not "operate on innuendo" and emphasising that there is no evidence that the Democratic presidential nominee violated the law.

"I do think that there is a norm that when there are investigations, we don't operate on innuendo, and we don't operate on incomplete information, and we don't operate on leaks," Obama told NowThis News.

"We operate based on concrete decisions that are made. When this was investigated thoroughly last time, the conclusion of the FBI, the conclusion of the Justice Department, the conclusion of repeated congressional investigations, was she had made some mistakes but that there wasn't anything there that was prosecutable."

The President's remarks came several days after FBI Director James Comey's surprise announcement that agents would review thousands of emails potentially connected to Clinton that were discovered as part of a separate inquiry into former congressman Anthony Weiner who is married to a high-ranking Clinton aide, Huma Abedin.

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"I've made a very deliberate effort to make sure that I don't look like I'm meddling in what are supposed to be independent processes for making these assessments," Obama said.

Of Clinton, he added: "Setting aside the particulars of this case, I know that she is somebody who has always looked out for the interests of America and the American people first."

Obama had not mentioned the case during recent appearances at Clinton campaign rallies in Florida and Ohio.

Comey's disclosure, made in a notice to Congress that leaked to reporters, has prompted strong criticism of the FBI from Democrats and some Republican lawmakers who have questioned whether Comey violated Justice Department policies by making a decision so close to Election Day that risked shaking up a political campaign.

Though the race between Clinton and Republican nominee Donald Trump already had been narrowing, according to public polls, Clinton has lost more of her lead since Comey's announcement.

RealClearPolitics, which averages most major opinion polls, showed Clinton's national lead had narrowed to 1.7 points today from 4.6 points last week.

A new Washington Post-ABC News Tracking Poll finds Trump now holds an edge on which candidate is honest and trustworthy, while 59 per cent disapproved of Clinton's handling of her email on a personal server while serving as Secretary of State.

Another new poll has Clinton leading Trump by six percentage points among likely voters.

It is the same advantage the Democratic presidential nominee held before the FBI announcement.

The Reuters/Ipsos daily tracking poll for October 29 to November 2 was conducted almost entirely after Comey notified Congress last week.

Among 1772 people who have either voted already or were identified as likely voters in the November 8 election, 45 per cent said they supported Clinton, while 39 per cent said they backed Trump. Last Friday Clinton led Trump by 43 per cent to 37 per cent.

In a four-way poll that included alternative party candidates, Clinton led Trump by 8 percentage points among likely voters.

Polls out today of swing states had mixed news for Clinton.

She is leading in the key states of Pennsylvania, North Carolina, Florida, Michigan, Virginia, Wisconsin and Colorado. But the polls show some evidence of tightening in Colorado, Pennsylvania and Virginia.

Trump is ahead in Ohio and Arizona.

LATEST POLLS
Florida
CNN - Clinton 49, Trump 47
Quinnipiac - Clinton 46, Trump 45
TargetSmart - Clinton 48, Trump 40

North Carolina
Quinnipiac - Clinton 47, Trump 44

Ohio
Quinnipiac - Trump 46, Clinton 41

Pennsylvania
Quinnipiac - Clinton 48, Trump 43
Monmouth - Clinton 48, Trump 44
CNN - Clinton 48, Trump 44
Susquehanna - Clinton 45, Trump 43

Nevada
CNN - Trump 49, Clinton 43
Political Polls - Clinton 45, Trump 38

Arizona
CNN - Trump 49, Clinton 44

Michigan
Mitchell - Clinton 50, Trump 43

Virginia
Winthrop - Clinton 44, Trump 39

Wisconsin
Marquette Law School - Clinton 46, Trump 40

Colorado
Emerson - Clinton 44, Trump 41
Political Polls - Clinton 44, Trump 37

Clinton painted a grim picture for minorities of life under a Trump presidency, as she sought to energise Democrats and sway undecided voters in the election's final days.

Clinton was campaigning in the West, both in battleground Nevada and in Arizona. The latter is a reliably Republican state where Democrats see an opening against Trump given his unpopularity with Hispanics.

Clinton urged voters in Las Vegas to imagine what life would be like if Trump is inaugurated. For Hispanics, she said, that would mean having a president "who doesn't see you as Americans". And for blacks, she said it would mean having a president who believes their lives are consumed by "crime and poverty and despair".

Washington Post, AAP