Millions of Americans were pouring into polling booths this morning (Hong Kong time) to decide one of the closest, most bitterly fought presidential elections in years.
With final polls too close to call between Democrat President Barack Obama and his Republican rival Mitt Romney, all eyes will be on 11 or so swing states - particularly Ohio and Virginia - that are vital to both candidates.
Thousands of voters were queuing at booths, some amid the rubble left by superstorm Sandy, as dawn broke bright but cold along the east coast.
Many expressed anger at a particularly nasty campaign that saw more than US$1 billion spent on often dishonest television campaigns as Obama painted Romney as far right and out of touch and Romney branded Obama an economic and political failure.
"It's been an awfully nasty campaign, so it is wonderful just to get out to vote and finally end this thing," said Washington voter Pam Sanders.
Obama was in tears on Monday as he staged the last act of his campaign in Iowa - the Midwestern state where he started his run for the presidency five years ago. Win or lose, the race will be the last election campaign for the 51-year-old former senator.
Romney appeared less wistful and more upbeat as he wrapped up his bid in the northeastern state of New Hampshire. "Stay with me until victory tomorrow night," he said.
Polls start to close in some eastern and Midwestern states from 6pm EST (7am Hong Kong), with the last booths shutting on the west coast six hours later.
With provisional results expected well before then from the key swing states, the winner may be apparent by 11pm local time.
If the race is really as close as national polls predict, it could be a different story. Neither candidate will want to repeat the mistake of the Democrat Al Gore when he conceded to Republican George W. Bush in 2000, only to retract it a few hours later. A protracted legal battle followed over recounts in Florida, settled only when the Supreme Court intervened to call a halt - securing a victory for Bush.
Already both campaign teams have assembled rival phalanxes of lawyers, many of whom are already scrutinising voting in the key swing states.
The first result of the election reflected the closeness in the polls. By tradition, votes were tallied in Dixville Notch and Hart's Location, New Hampshire, shortly after midnight. Obama and Romney each received five votes in Dixville Notch - the first tie there in history. In Hart's Location, Obama got 23 votes to nine for Romney and two for Libertarian candidate Gary Johnson.
The Democratic Party is expected to keep its control of the US Senate and the Republicans the US House of Representatives - with both having to confront the looming "fiscal cliff" as soon as the election ends.
Additional reporting by Reuters