Voting is underway in 26 states in the United States as Americans go to the polls to choose their next president.
The race is keenly divided between Democratic candidate, President Barak Obama, and Republican challenger, Mitt Romney.
As many as 30 million voters have already cast their ballots, with more than 30 states allowing either absentee voting or in-person early voting, BBC reports.
On the stroke of midnight, the first votes were cast and quickly counted in the tiny village of Dixville Notch in New Hampshire.
They resulted in a tie with five votes each for Obama and Romney.
Polling stations will begin closing in eastern states at 19:00 EST (00:00 GMT).
Polling stations have opened on the East Coast and in parts of the Midwest – a winner could be known by midnight.
The voting ends a hard-fought race that began nearly two years ago and has cost more than $2bn (£1.3bn).
Polls show the race is neck and neck, although the president holds a slender polling lead in crucial swing states.
National polls by Washington Post/ABC News and the Pew Research Centre both give Obama a three-point edge over his rival.
The election is decided by the electoral college. Each state is given a number of electoral votes in rough proportion to its population.
The candidate who wins 270 electoral votes – by prevailing in the mostly winner-take-all state contests – becomes president.
Also on Tuesday’s ballot are a handful of state governors, one third of the seats in the 100-member US Senate and all 435 seats in the House of Representatives.
Republicans are expected to keep control of the House, while Democrats were tipped to do the same in the Senate, BBC projects.
In 34 states, plus the District of Columbia, early voting has been under way for several days, even weeks.
Some 31 million ballots have already been cast – but none will be counted until today.
Paul Vassile of the BBC tweets, “Voting in Central Harlem, 140th st. Long lines, few machines. Very small room that is overcrowded and people frustrated. Democracy in action.”