Economy is main issue with US voters, exit poll finds
Most eve-of-election polls showed Mr Obama with a razor-thin lead over Mr Romney. The winner will be determined by who gets 270 electoral college votes; most polling experts agree Mr Obama has more paths to get there.
A final national NBC/Wall Street Journal poll showed Mr Obama had the support of 48 per cent of likely voters, with Mr Romney on 47 per cent, within the margin of error. Real Clear Politics, which provides an aggregate of published polls, indicated Mr Obama was marginally ahead in all but two battleground states, Florida and North Carolina.
Whichever candidate wins, a razor-thin margin might not bode well for the clear mandate needed to help break the partisan gridlock in Washington.
In a frantic final day of campaigning, both candidates predicted the winner would be determined by which of their operations could get the most supporters to the polls. “This is going to be a turnout election,” Mr Obama said.
At a rally in Virginia, featuring an enormous “Get Out and Vote” banner, Mr Romney said: “We have one job left and that’s getting people out to vote.” In response, the crowd chanted “One more day!”
Both Mr Obama and Mr Romney continued to present themselves as the real agents of change while painting the other as a return to the status quo.
US vice president Joe Biden has cast his vote in the election at a school in Greenville, Delaware, saying “it’s always a kick”.
Mr Biden shook hands with and hugged other voters as he waited. He urged Americans to vote “even if you have to stand in line”.
Both candidates meanwhile sought to benefit from some star power. Mr Romney was joined in New Hampshire by Kid Rock while Mr Obama had rapper Jay-Z with him in Columbus and Bruce Springsteen as his warm-up act.
Under the US system, the winner of the presidential election is not determined by the nationwide popular vote but in state-by-state contests. The candidate who wins a state - with Maine and Nebraska the exceptions - is awarded all of that state’s electoral votes, which are apportioned based on representation in Congress.
In 2008, an estimated 130 million people voted, a turnout of about 55 per cent but that could be down slightly this year.
More than 30 million people have already voted in 34 states, either by post or in person.