America's presidential candidates Barack Obama and Mitt Romney have made their final pitch to voters ahead of polling day.
National polls show the men in a statistical dead heat, although Mr Obama enjoys a narrow lead in some of the all-important battleground states.
Both spent the day before Tuesday's election visiting key swing states and making final pitches to voters, the BBC reports.
Mr Romney went to Florida, where polls suggest he has the edge, and then to Virginia, New Hampshire and Ohio. Mr Obama appeared in Iowa, Wisconsin and Ohio.
The election will be decided in just a handful of states, with Ohio in particular seen as crucial to victory.
Barack Obama closed his re-election campaign in Des Moines, Iowa - the city where his bid for the presidency began in early 2007.
At a late-night rally on Monday, he told the crowd that Iowa had started "a movement that spread across the country".
Republican Mitt Romney, meanwhile, was due to end his campaign with a late-night rally in New Hampshire but made the surprise announcement that he would extend campaigning into election day itself - visiting Ohio and Pennsylvania on Tuesday.
Mr Romney would become the first Mormon president of the United States if he wins.
First votes cast
The first votes have been cast on polling day in the tiny New Hampshire town of Dixville Notch.
The town's vote, held shortly after midnight on Tuesday (local time), was quickly counted, with Mr Obama and Mr Romney each receiving five votes. It is the first time in the town's history that the result has been tied.
Meanwhile, 30 million Americans have already cast their ballot through early voting across 34 states. In the 2008 presidential election, 130 million people voted.