Democratic presidential nominee Hillary Clinton leads Republican Donald Trump by just two percentage points in two polls released this evening.
Mrs Clinton leads Mr Trump by two percentage points in a four-way race, according to a Fox News opinion poll released today.
The poll of 1,211 registered voters was conducted Tuesday to Thursday and had a margin of error of plus or minus 2.5 percentage points, Fox News said.
Mrs Clinton had 45% support and Mr Trump had 43%.
In a McClatchy-Marist poll, Mrs Clinton also leads Mr Trump by two percentage points. The previous McClatchy-Marist poll showed Mrs Clinton leading by seven percentage points.
Democrats are nervously eyeing opinion polls that show Mrs Clinton has a tenuous lead over Mr Trump as both candidates race through vital battleground states in the hope of winning crucial votes.
The race for the White House has tightened significantly in the past week, with several swing states that Mr Trump must win shifting from favouring Mrs Clinton to toss-ups, according to the latest Reuters/Ipsos States of the Nation project.
The project, a survey of about 15,000 people every week in all 50 states plus Washington DC, found the two candidates were now tied in Florida and North Carolina and that Mrs Clinton's lead in Michigan had narrowed so much the state was too close to call.
Ohio remained a dead heat, with Pennsylvania now tilting to Mrs Clinton.
A Reuters/Ipsos national daily tracking poll found on Wednesday that Mrs Clinton was leading Mr Trump by six percentage points, the same advantage she held before FBI Director James Comey sent a letter to Congress last week saying the agency had found a new cache of emails potentially related to its probe of Mrs Clinton emails.
Other polls have shown a far closer race, fueling Democratic worries about the state of the race just five days before Tuesday's election.
Mrs Clinton's national lead over Mr Trump eroded to three percentage points among likely voters in a New York Times/CBS News poll yesterday, down from nine points just two weeks ago.
An average of polls compiled by the RealClearPolitics website also showed her lead at 1.7 percentage points, well down from the solid advantage she had until late last month.
Nevertheless, some polls showed Mrs Clinton recovering slightly from her slide in the past week.
She has maintained her comfortable edge in the Reuters/Ipsos poll and inched back into a two-point lead over Mr Trump in the latest Washington Post-ABC Newstracking poll, which had shown her falling slightly behind Mr Trump earlier this week.
US President Barack Obama, on the third day of a multi-state campaign trek for Mrs Clinton, adopted a sense of urgency before a raucous crowd at Florida International University.
"You have the chance to shape history," Mr Obama said.
"There are times where history is ... moveable. Where you can make things better or worse. This is one of those moments."
The tightening White House race has rattled financial markets as investors weigh a possible Trump victory.
Investors have generally seen Mrs 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.
Melania Trump addressed Republicans at a campaign-trail appearance in Philadelphia last night pic.twitter.com/hsl2OWeZ62
— RTÉ News (@rtenews) November 4, 2016
Meanwhile, Mr Trump's wife Melania made her first campaign-trail appearance of the election campaign when she addressed Republican's in Philadelphia.
"We must win on November 8 and we must come together as Americans. We must treat each other with respect and kindness even when we disagree," she said in Berwyn, Pennsylvania.
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
