Hillary Clinton and Donald Trump were running neck and neck in early results as polling stations closed in the eastern United States, with the world waiting anxiously to see who will win the historic White House clash.
A deeply divided electorate of about 200 million Americans were asked to make a momentous choice between electing the nation's first woman president, or handing the reins of power to a billionaire populist who has upended US politics with his improbable outsider campaign.
With voting over in a handful of states and Americans still lining up to cast their ballots farther west, television networks called eight states so far for the Republican Trump -- Alabama, Indiana, Kentucky, Mississippi, Oklahoma, South Carolina, Tennessee and West Virginia.
Clinton was also credited with eight states -- Connecticut, Delaware, Illinois, Maryland, Massachusetts, New Jersey, Rhode Island and Vermont --as well as the capital, Washington DC, giving her a notional lead in terms of electoral college votes.
But all eyes were on the tight race in Florida, a must-win race for Trump, who would find it hard to cobble together a majority without the Sunshine State's 29 electoral college votes.
If Florida goes to Clinton, the next big challenge will be Pennsylvania, which will likely decide the result of the long, bruising contest for the right to lead the world's biggest economy.
At the venue where Trump will hold his planned victory party in New York and in the bar at Trump Tower, his home and headquarters, supporters were upbeat, expressing confidence that he would stage a major political upset.
Cheers erupted when one network update showed Trump slightly ahead in Florida. "This is like a football game. I'm going to have a heart attack," said 76-year-old Mike Garcia, a Republican from Pennsylvania.
Across town at the huge conference center where Clinton hopes to hold her victory rally, supporters were just as giddy.
"Hillary's going to win and we're going to unite America," declared Jade Wiederholt, a 43-year-old marketing consultant from New York, expressing frustration with the long slog to the polls.
"America is ready for it to be over and we move forward."
Earlier, Clinton and her husband Bill, the former president, voted near their home in Chappaqua, before emerging to shake hands and chat with the crowd.
"So many people are counting on the outcome of this election, what it means for our country," the 69-year-old secretary of state said. "And I'll do the very best I can if I'm fortunate enough to win today."
An exit poll by CNN however found that only four in 10 voters were optimistic that incumbent president Barack Obama's successor would do any better than he has during his two terms in office.
- 'Don't let up' -
Trump, 70, cast his ballot alongside his wife Melania in a Manhattan school gymnasium.
"Right now it's looking very good," he told reporters -- paying no heed to protesters who welcomed him with chants of "New York hates you!"
But as the clock ticked down towards the close of polling, the Republican issued a last-minute appeal to voters, especially in Florida -- without which his path to the presidency is slim at best.
"Don't let up, keep getting out to vote - this election is FAR FROM OVER! We are doing well but there is much time left. GO FLORIDA!" Trump tweeted -- looking to garner 11th hour votes.
- Marathon campaign -
The 2016 race was the most bruising in modern memory.
Obama's election eight years ago as the nation's first black president had raised hopes of uniting Americans, but the current contest has only highlighted the country's divisions -- and the fact that voters are not necessarily happy with their options.
Exit polls by ABC News and NBC News found that both Clinton and Trump are seen as untrustworthy by majorities of voters, while most find Trump's temperament unpresidential.
Most voters told ABC that the economy was the most important issue or them, but were evenly divided on which candidate would handle it better, so the final result may come down to turnout.
The exit polls, and reports coming in from polling stations around the country, suggested that Latino turnout was high and that this would favor Clinton over the anti-immigration candidate, Trump.
Trump's campaign spooked world markets seeking stability after the recent global slowdown, but stocks rose for a second straight day Tuesday on the expectation that Clinton will prevail.
At the closing bell, the S&P 500 closed up 0.4 percent.
- 'La Senora' -
A polling average by tracker site RealClearPolitics gave Clinton a 3.3-percentage point national lead, but Trump had the advantage in several of the swing states that he must conquer to pull off an upset.
Early voting has shown particular enthusiasm among Hispanic voters, an increasingly influential voting bloc whose strong turnout could shape Tuesday's results.
In the heavily Latino neighborhood of East Los Angeles, Mexican-Americans Margarito Salinas, 88, and friend Guadalupe Cobian, 64 said their choice was an easy one.
"That guy is a Nazi," Salinas said of Trump. "My vote is for La Senora."
- 'Big-hearted' -
Clinton conducted six radio interviews in the lull after casting her ballot, when candidates suddenly have hours of downtime following a non-stop campaign that ended in the early hours of Tuesday.
She has urged citizens to vote for a more "big-hearted" America.
"I hope to be remembered as someone who began to help heal our country, to overcome the divide, the very unfortunate feeling that a lot of people have that this election was very much filled with nastiness and negativity," she told WOKQ.
Trump pressed his message with voters who feel left behind by globalization and social change, wrapping up with a flourish in Michigan after midnight and predicting a historic upset.