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 3 percentage points among 1,333 registered voters in the Times/CBS poll taken Oct. 28-Nov. 1. The Federal Bureau of Investigation announced on Oct. 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 3 percentage points, showed Clinton with 45 percent support compared to 42 percent 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. More detailed results from the poll were expected later on Thursday.
Separately, a Washington Post/ABC poll showed Clinton 2 percentage points ahead among 1,767 likely voters surveyed Oct. 29 - Nov. 1, 47 percent to Trump's 45 percent. It also had a margin of error of plus or minus 3 percentage points.
A Reuters/Ipsos poll on Wednesday found Clinton leading Trump by 6 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.
The tightening White House race has rattled financial markets as investors weigh a possible Trump victory. Investors have generally seen Clinton as the candidate who would maintain the status quo, while there is more market uncertainty over what a Trump presidency might mean in terms of economic policy, free trade and geopolitics.
Market nerves over the US election were eclipsed on Thursday by a UK court ruling that parliament must approve a government decision to trigger Brexit, or the exit from the European Union.
NORTH CAROLINA COUNTS
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 called on a crowd of about 15,000 at Arizona State University to imagine life with a Trump presidency, particularly for women, Latinos and Muslims.
Trump, a New York businessman who has never previously run for political office, has caused frequent offence during his unorthodox campaign, while winning support for his promises to upend politics as usual in Washington.
"What would your life be like if he were in the White House?" Clinton said. "And the truth is we really don’t have to guess. We just have to look at everything he has said and done in his career and this campaign, it’s a good preview of what would likely happen,” she said.
“If you add up all of the people and all the groups of people he has insulted and demeaned it makes way more than half of America,” Clinton added.
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.
On Thursday, Clinton holds two events on Thursday in North Carolina, where early voting has already started in the race for the southern state's 15 electoral votes.
Trump also has three events scheduled in the state after urging supporters at a rally in Miami on Wednesday to turn out and vote.
Florida, like North Carolina, is considered a must-win state for the presidential contenders.
President Barack Obama has scheduled a stop in Jacksonville later on Thursday to stump for Clinton as part of his campaign swing this week that also included stops in North Carolina and Ohio.
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 percent, the RealClearPolitics average showed.
Polls of other key battleground states also show a tight race in Ohio, Pennsylvania, Colorado and Nevada, among others.
