Millions of Americans are voting in an historic election that could put Donald Trump back into the White House or make Kamala Harris the first woman to become US president.
The two candidates are neck and neck in the polls after bitter campaign that saw two assassination attempts against Republican Mr Trump as well as the shock withdrawal of President Joe Biden.
In around 100 days, Ms Harris has found her feet and mounted a fierce challenge to her opponent.
With just hours left before polls close, the election has come down to the wire and could be decided by a handful of crucial battleground states.
Follow live: Harris makes surprise stop in Washington
Voting on Tuesday appears to be smooth, with only scattered reports of delays from extreme weather, long lines or technical problems.
The FBI reported that there had been “non-credible” bomb threats to several states, some of which it said came from Russian email domains.
Pic: AP
How the vote works
As well as those lining up at polling booths on Tuesday, tens of millions of Americans cast early ballots – voting by post or in person before today.
To become president, the winning candidate needs 270 electoral votes or more, with each state carrying a different number of votes.
If the polls predicting a close race are correct, the election will likely come down to a few battleground states: Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin.
The first ballots cast on Tuesday mirrored the national divide. Overnight, the six registered voters in the tiny hamlet of Dixville Notch, New Hampshire, split their votes between the two candidates in voting just past midnight.
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Key issues for American voters
Read more:
An easy guide to the US election
What Trump or Harris victories would mean for UK
Trump or Harris
Former President Mr Trump, 78, voted in Palm Beach, Florida, near his Mar-a-Lago club.
Wearing his trademark red “Make America Great Again” baseball cap, he said at the polling station that he was feeling “very confident”.
“I hear we’re doing very well,” he said. “It looks like Republicans have shown up in force.”
According to The New York Times, Elon Musk, the world’s richest man and Trump donor, will watch results unfold with the former president.
In the meantime, Ms Harris, the 60-year-old Democratic vice president, did radio interviews in the battleground states of Pennsylvania, Georgia and North Carolina.
A cat seen at a polling booth in battleground state Pennsylvania. Pic: Reuters
What do the polls say?
Many polls are too tight to call and, with a large margin of error, most experts are refusing to predict the outcome.
Georgia could be among the first battleground to declare, with polls there closing at 7pm local time (midnight UK time). State election officials told Sky News they could have a result as early as 10pm (3am UK time).
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North Carolina could also give an early indication of how the vote is going.
Even so, it could be several days before the US has a definitive result.
Voters are not just selecting a president. A number of seats in the House of Representatives and the Senate are up for grabs. In addition, 10 states will hold abortion-related ballots, half of which would overturn existing restrictions.