The most unlikely presidential candidate in recent history surged ahead in early voting as Donald Trump swept to a quick advantage over Hillary Clinton - securing the battleground state of Ohio and Florida.

After millions of Americans turned out to vote in numbers that may have set a record, Mr Trump was performing far better than than many expected - certainly better than most pundits had anticipated - in all the crucial states and was on track for the White House.

At 11.55pm Eastern Standard Time, CNN scored the electoral college race 232 to 209 in favour of the New York tycoon. He was reckoned to have secured 23 states, to 17 for Ms Clinton - including other swing states such as North Carolina.

Picture: (Chip Somodevilla/Getty Images)

As financial markets around the world tumbled in anticipation of a possible victory for Mr Trump, Ms Clinton was left needing to win the remaining safe Democratic states and all of the remaining competitive ones. This included Michigan, where Mr Trump had a slim lead with nearly 70 per cent of precincts reporting. The state would appear to be key for Ms Clinton, with New Hampshire also potentially important. In New Hampshire Mr Trump again has a slim lead, with more than 75 per cent of precincts reporting. Ms Clinton was ahead in Nevada, another state she must take.

However, supporters of Ms Clinton appeared increasingly anxious.

“I went and voted at 12pm. The polling station was near my dorm,” said Gertrude Clark, a 19-year-old student in New York. She said she had voted for Ms Clinton, as she would prefer a politician to run the country rather than a businessman. “She is not a saint,” she added. “But sometimes you have to pick the better of two opticians.

Isra Ali, an academic had voted early in Jersey City. But she said that even at 6.30am, the number of people was greater and usual and she sensed an amount of tension.

“I voted for Hillary Clinton. As a Muslim American I’m terrified of Donald Trump becoming president,” she said. “I don’t agree with everything that she does, but she is the best choice.”

Mr Trump, 70, voted in New York, where he was booed by some in the polling and where he was photographed glancing over his wife’s shoulder, as she cast her ballot, an image that quickly went viral.

Mr Trump once again raised the prospect that the vote would not be fair.

“We’re going to see how things play out today. Hopefully they’ll play out well and hopefully we won’t have to worry about it, meaning hopefully we’ll win,” he told Fox News. “I want to see everything honest.”

Florida last recounted votes in a presidential election in 2000 (AP)

Mr Trump also tried to sue the registrar of voters in Nevada’s Clark County over a polling place in Las Vegas that had been allowed to remain open late last week during an early voting period to accommodate people, many of them Hispanic, who were lined up to cast ballots.

If successful, the lawsuit would have asked that records of thousands of early votes would be discounted. But the judge, Gloria Sterman, said that the case was “disturbing to me” and make clear that she was not doing it.

Ms Clinton, aiming to become the first woman US president, cast her ballot at an elementary school near her home in Chappaqua, New York early on Tuesday morning.

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“It is the most humbling feeling. I know how much responsibility goes with this,” she told Reuters. “So many people are counting on the outcome of this election, what it means for our country. And I'll do the very best I can if I'm fortunate enough to win today.”