The US is voting in one of the most divisive presidential elections in decades, pitting incumbent Republican Donald Trump against his Democratic challenger Joe Biden.
The first polls opened from 05:00 EST in Vermont.
Nearly 100 million Americans have already cast their ballots in early voting, putting the US on course for its highest turnout in a century.
Both rivals spent the final hours of the race rallying in key swing states.
National polls give a firm lead to Joe Biden, but it is a closer race in the states that could decide the outcome.
Among the first states to begin election-day voting on November 3 are the key battlegrounds of North Carolina and Ohio, followed half an hour later by Florida, Pennsylvania, Georgia, Michigan and Wisconsin. Arizona will follow.
To be elected president, a candidate must win at least 270 votes in what is called the electoral college. Each state gets a certain number of votes partly based on its population and there are a total of 538 up for grabs.
This system explains why it is possible for a candidate to win the most votes nationally – like Hillary Clinton did in 2016 – but still lose the election.
The coronavirus pandemic has hung over the election campaign, with the epidemic in the country worsening over the final weeks of the race. The US has recorded more cases and more deaths than anywhere else in the world, and fear of infection has contributed to an unprecedented surge in early and postal voting.
As the nation counts down the hours to the vote, there are fears that pockets of post-election violence could break out.
A new “non-scalable” fence has been put up around the White House in Washington DC. Businesses in the nation’s capital and also in New York City have been seen boarding up their premises due to concerns about unrest.
On November 2, President Trump sprinted through four more battleground states.
In North Carolina, the president told supporters that “next year will be the greatest economic year in the history of our country”. Economists however warn the damage inflicted by the coronavirus pandemic – the biggest decline in the US economy in more than 80 years – could still take years to overcome.
After North Carolina, Donald Trump headed to Scranton, Pennsylvania, the city where his opponent lived until he was 10. At a rally there he reminded his supporters that he won the state in 2016, despite polls suggesting he would lose.
Joe Biden also went to Pennsylvania where he was joined by singer Lady Gaga at a rally in Pittsburgh. Musician John Legend addressed voters with vice-presidential candidate Kamala Harris.
In Ohio, Joe Biden repeated the core message of his campaign, telling voters that the race was about the soul of America. He said it was time for President Trump to “pack his bags”, saying “we’re done with the tweets, the anger, the hate, the failure, the irresponsibility”.
On November 2, Donald Trump also held rallies in Traverse City, Michigan, and Kenosha, Wisconsin. Kenosha was rocked by violent protests in August after the police shooting of a black man.
In Traverse City the president asked for the votes of black Americans.
He travelled to Grand Rapids, Michigan for his last rally, the same city where he held the final event of the 2016 election race.
In the last hours of the campaign, Twitter and Facebook labelled a post by President Trump as “misleading”, after he claimed that postal ballots in the key state of Pennsylvania could lead to rampant fraud. They also added a link to a website explaining why mail-in votes were safe.
It came after the Supreme Court allowed Pennsylvania to count postal ballots received three days after the election.
President Trump and his campaign have indicated they will sue to block the move.
Legal fights over ballots have also been unfolding in Minnesota, North Carolina and Texas.
When will we get a result?
It can take several days for every vote to be counted after any presidential election, but it is usually pretty clear who the winner is by the early hours of the following morning.