US Election: Hillary Clinton or Donald Trump? Counting Begins.

NEW YORK: Polls began to close in the long and bitter race for the White House between Democrat Hillary Clinton and Republican Donald Trump on Tuesday, with last-minute opinion polls giving Clinton the edge in the final hours of the race.

Polls in the Eastern time zones of Indiana and Kentucky were the first to close, and a flood of vital battleground states such as Virginia, North Carolina and Ohio - where polls were due to close in the next 90 minutes - would provide initial clues of the possible winner.

Clinton led Trump, 44 per cent to 39 per cent, in the last Reuters/Ipsos national tracking poll before Election Day. A Reuters/Ipsos States of the Nation poll gave her a 90 percent chance of defeating Trump and becoming the first woman elected US president.

The campaign focussed on the character of the candidates: Clinton, 69, a former US secretary of state, and Trump, 70, a New York businessman. Each accused the other of being fundamentally unfit to lead the United States or to deal with such challenges as an arduous economic recovery, Islamist militants and the rise of China.

Trump again raised the possibility on Tuesday of not accepting the election's outcome, saying he had seen reports of voting irregularities. He gave few details and Reuters could not immediately verify the existence of such problems.

Financial markets, betting exchanges and online trading platforms largely predicted a Clinton win, although Trump's team said he could pull off a surprise victory like the June "Brexit" vote to pull Britain out of the European Union.

Voters appeared to be worried about the country's direction and were seeking a "strong leader who can take the country back from the rich and powerful," according to an early reading from the Reuters/Ipsos national Election Day poll.

The poll of more than 10,000 people who voted in the election showed a majority worried about their ability to get ahead, with little confidence in political parties or the media to improve their situation.

A strong turnout of voters for Clinton could jeopardise Republican control of the US Senate, as voters choose 34 senators of the 100-member chamber on Tuesday. Democrats needed a net gain of five seats to win control. All 435 seats in the House of Representatives were being contested. The House was expected to remain in Republican hands.

The Dow Jones Industrial Average index ended up 0.4 per cent as investors bet on a win for Clinton, seen by Wall Street as more likely to ensure financial and political stability. Mexico's peso hit a two-month high on Tuesday on the expectation of a loss for Trump, who has vowed to rip up a trade deal with Mexico.