NEW YORK – Hillary Clinton and Donald Trump have been locked in a dead heat in their historic clash for the White House, as the world waited anxiously for results from the key battleground states that will decide the winner.

A deeply divided electorate of about 200 million Americans on Tuesday 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 most eastern states and Americans still lining up to cast their ballots on the West Coast, television networks called 16 states so far for the Republican Trump - a band of red on the electoral map stretching from South Carolina to Texas.

Clinton was credited with nine states - Connecticut, Delaware, Illinois, Maryland, Massachusetts, New Jersey, New York, 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 challenges will be Pennsylvania, Ohio and Virginia - states that will likely decide the result of the long, bruising contest for the right to lead the world’s biggest economy.

On the legislative side, the Republicans were on course to retain their majority in the US House of Representatives, according to network projections - a situation that has been a thorn in the side of incumbent US President Barack Obama.

Dueling Manhattan parties

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.

Clinton tweeted: "This team has so much to be proud of. Whatever happens tonight, thank you for everything."

She and her husband, former president Bill Clinton, huddled in a hotel near the venue to prepare a victory - or concession - speech.

’I’ll do the very best I can’

Earlier, the Clintons 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 former 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 Obama’s successor would do any better than he has during his two terms in office.

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!"

Tough contest

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 per cent. But Asian markets were open as polls closed and the situation was much less clear cut, with equities falling after initial gains.

’Big-hearted’

Early voting has shown particular enthusiasm among Hispanic voters, an increasingly influential voting bloc whose strong turnout could shape the results.

Clinton has urged citizens to vote for a more "big-hearted" America, while Trump has vowed to tear up US trade deals, control immigration, restore manufacturing jobs that moved abroad and to: "Make America great again". – AFP