Democrat Hillary Clinton and Republican Donald Trump face voters on Tuesday as millions of Americans turn out on Election Day to pick the next U.S. president and end a bruising campaign that polls said favoured Clinton.
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.
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.
World markets braced for the outcome of one of the most contentious U.S. presidential elections in history, with stocks up slightly on cautious expectations of a Clinton win. The dollar and bond yields slipped, while gold inched up.
Clinton arrived to cast her ballot at an elementary school in her hometown of Chappaqua, New York, on Tuesday morning.
Trump, who planned to vote later in Manhattan, began Election Day with a ritual call to the "Fox & Friends" morning news show. "I'm a little bit superstitious," he said. "I've won many primaries speaking to you first in the morning.
Each then hoped to hold an evening victory rally about a mile in New York City.
The final week of campaigning was a grinding series of get-out-the-vote rallies across battleground states where the election is likely to be decided.
"We choose to believe in a hopeful, inclusive, big-hearted America," Clinton said in Philadelphia before a crowd of 33,000 - the largest of her campaign.
She was joined by Democratic President Barack Obama; his wife, Michelle; and Clinton's husband, former President Bill Clinton, along with singers Jon Bon Jovi and Bruce Springsteen.
She later made another star-studded appeal in Raleigh, North Carolina, flanked again by Bon Jovi and by Lady Gaga in a midnight rally.
At an evening rally in Manchester, New Hampshire, Trump brought much of his family and running mate Mike Pence on stage. The raucous event in the state that gave Trump his first primary win featured a fog machine and red-white-and-blue lasers.