Democrat Hillary Clinton and Republican Donald Trump are heading to North Carolina in a final effort to shore up support in the swing state as two polls show Clinton maintaining a narrow lead nationally just days ahead of the presidential election.

LISTEN ABOVE: Michelle Rindels (AP reporter in Nevada) and Mark Caputo (Politico reporter in Florida) speak to Rachel Smalley about the mood in swing states

The surveys by the New York Times/CBS and the Washington Post/ABC echoed other national polls that have shown Clinton with a slimmer lead over Trump since the re-emergence last week of a controversy over her use of a private email server while secretary of state.

Clinton led by three percentage points among 1333 registered voters in the Times/CBS poll taken between October 28 and Novovember 1.

The Federal Bureau of Investigation announced on October 28 that it was reviewing a new batch of emails that might be related to her email practices.

The survey, with a margin of error of plus or minus three percentage points, showed Clinton with 45 per cent support compared to 42 per cent for Trump, according to the Times.

"About six in 10 voters over all said that the 11th-hour disclosures about each candidate would make no real difference in their vote," the Times said.

There were also strong differences by gender, with more women supporting Clinton and Trump leading among men.

Separately, a Washington Post/ABC poll showed Clinton two percentage points ahead among 1,767 likely voters surveyed at 47 per cent to Trump's 45 per cent. It also had a margin of error of plus or minus three percentage points.

A Reuters/Ipsos poll on Wednesday found Clinton leading Trump by six percentage points, the same advantage she held before FBI Director James Comey released his letter.

An average of polls compiled by RealClearPolitics website showed Clinton ahead by 1.7 percentage points on Thursday, well down from the solid lead she had until late last month.

Clinton, a former secretary of state hoping to become the first woman to be elected US president, was in Arizona on Wednesday evening, addressing one of her largest rallies to date.

She and Trump are focused heavily on states where the race is close, given the White House is decided by the Electoral College system of tallying wins on a state-by-state basis.

Florida, like North Carolina, is considered a must-win state for the presidential contenders. A RealClearPolitics average of polls in the Florida, which carries 29 electoral votes, put Trump 0.7 point ahead of Clinton.

In North Carolina, the race is tied with both Clinton and Trump at 46 per cent, the RealClearPolitics average showed.

Polls of other key battleground states also show a tight race in Ohio, Pennsylvania, Colorado and Nevada, among others.