Polling stations have opened as the first ballots were cast in one of the most divisive US presidential elections, pitting Democratic nominee Hillary Clinton against her Republican rival Donald Trump.

The kick-off in the early hours of Tuesday marked the end to a bitter campaign as Clinton and Trump presented radically different visions of how to lead the US.

A Reuters/Ipsos States of the Nation poll gave Clinton a 90 percent chance of defeating Trump and said she was on track to win 303 electoral college votes out of 270 needed, to Trump's 235.

The Democratic nominee voted with husband Bill Clinton at an elementary school near their home in Chappaqua, New York state.

Hillary Clinton was accompanied by her husband, Bill, and senior aide Huma Abedin, far left [Andrew Harnik/AP]

"I'm so happy, I'm just incredibly happy," said a smiling Clinton as she emerged from the polling station, shaking hands, mingling and chatting with the crowd.

Trump was expected to vote later on Tuesday in Manhattan, New York.

In a battle centred largely on the character of the candidates, Clinton, 69, a former secretary of state and first lady, and Trump, 70, a New York businessman, made their final, fervent appeals to supporters late on Monday to turn out the vote.

On Monday night, Clinton's lead over Trump had widened to 3.2 percent, according to an average of polls conducted by the website RealClearPolitics.

The figure came a day after the FBI announced that it had found no criminal wrongdoing in Clinton's use of a private email server, following a last-minute review that clouded her campaign and allowed Trump to recover ground lost in a series of recent scandals.

Campaigning in the state of Pennsylvania on Monday, Clinton promised to build a "big-hearted" America.

"Our core values are tested in this election," she said, adding that Americans should not accept "a dark and divisive vision" but "a hopeful, inclusive and a big-hearted America".

Al Jazeera's Kimberly Halkett, reporting from Philadelphia, said Clinton made the argument that she would be a president who would not divide but unite the country.

"Clinton said division would be the outcome of a Trump presidency," she said.

'Totally rigged system'

Trump delivered a speech in the crucial state of Florida, rallying against Washington, the medical care system and Clinton, telling his supporters it was their last chance to change a broken political system.

"Hillary Clinton is being protected by a totally rigged system," he said, questioning the legitimacy of the FBI's rapid review of a Clinton aide's emails and targeting what he called "the Washington establishment".

Latinos in Arizona campaign against Trump

"My contract with the American voter begins with a plan to end government corruption, and take back our country ... from the special interests who I know so well. When we win tomorrow, we are going to drain the swamp."

Al Jazeera's Alan Fisher, reporting from New Hampshire, said Trump's closing message stressed that Clinton was not fit to be president as she was enmeshed in various corruption scandals.

"Trump also said he would repeal and replace Obamacare, the Affordable Care Act as it is officially known in the US. And he said he would bring jobs and energy to the country," our correspondent said.

Both Clinton and Trump are by far the most unpopular candidates to run for the Oval Office in the past 30 years, according joint polling by ABC News and The Washington Post newspaper.

Since announcing his presidential campaign in June 2015, Trump, a billionaire businessman from New York, has consistently  alienated minority groups, refused to release his tax returns, and remained seemingly unapologetic for leaked tapes in which he brags about sexually assaulting women.

READ MORE: Understanding Donald Trump's candidacy

Clinton, who has 30 years in public service and has served as a state senator, secretary of state and first lady, is not wildly popular either.

Her campaign has been marred by the never-ending email scandal, accusations of negligence in  Benghazi, Libya, and for a recent gaffe in which the candidate said half of Trump's supporters belonged in a "basket of deplorables".

If she wins Clinton will become the first female US president.

What will the US election mean for immigrants?

Source: Al Jazeera News And Agencies