Donald Trump and Hillary Clinton have cast their votes as one of the most divisive and bitterly fought elections in modern American history nears its climax.
Tens of millions of voters across the United States are deciding on the next occupant of the White House as polling stations opened across the country.
Heavily armed police joined Republican Mr Trump as he voted at Public School 59 in Manhattan, a short distance from Trump Tower.
Hundreds of people watched from the street as Mr Trump was greeted by a mixture of boos and cries of "Donald, Donald".
Earlier Democratic candidate Mrs Clinton was joined by her husband Bill as she voted in Chappaqua, New York.
Mr Trump arrived at the polling station with his wife Melania and daughter Ivanka, shortly after two topless female protesters had been removed from the building.
Speaking before he voted, Mr Trump told Fox News: "I see so many dreams out there that didn’t happen, that could have happened with leadership, proper leadership.
"People are hurt so badly."
Mrs Clinton is aiming to become the first female president in US history, while Mr Trump hopes his pledge to Make America Great Again will win over voters in key swing states.
Victory for Mrs Clinton would see her follow husband Bill into the White House, with the former president becoming the first gentleman - or "first laddie", as some have suggested.
Mr Trump, who has been dogged by allegations of misogyny and sexual misconduct, has targeted battleground states in an effort to get the 270 electoral college votes he needs to become one of the most unlikely victors of a presidential race.
Both candidates will be in New York on election night, with the Republican billing his planned event at a Hilton hotel as a "victory party".
There was a heavy police presence in the city after US authorities received intelligence of a possible pre-election al Qaida attack, and more than 5,000 police officers have been assigned to secure central Manhattan.
Long queues were reported at polling stations across the country with a high turnout expected, while almost 45 million people cast ballots before election day.
After voting in her home town of Chappaqua, Mrs Clinton said: "I know how much responsibility goes with this. So many people are counting on the outcome of this election, what it means for our country, and I will do the very best I can if I’m fortunate enough to win today."
With polls suggesting Mrs Clinton had a narrow lead before election day, Donald Trump Jr said his father would concede defeat if he loses, provide the result is "legit and fair".
He told MSNBC: "All we’ve wanted is a fair fight. If he loses and it’s legit and fair, and there’s not obvious stuff out there - without question, yes."
Mr Trump has previously said he may not concede defeat in the election after complaining of a "rigged system", and later claimed he would accept the result if he won.
President Barack Obama, who will remain in the White House until January 20, took to Twitter to urge Americans to vote.
He tweeted: "Progress is on the ballot. Go vote - then make sure your friends, your family, and everyone you know votes too."