The dizzying presidential contest between Republican Donald Trump and Democrat Kamala Harris hurtled toward an uncertain finish on Tuesday as millions of Americans headed to the polls to choose between two sharply different visions for the country.

A race whipsawed by unprecedented events - two assassination attempts against Trump, President Joe Biden's surprise withdrawal and Harris' rapid rise - remained too close to call, even after billions of dollars in spending and months of frenetic campaigning.

The first ballots cast on election day mirrored the nationwide divide. Overnight, the six registered voters in the tiny hamlet of Dixville Notch, New Hampshire, split their votes between Harris and Trump in voting just past midnight.

Elsewhere on the East Coast, polls began opening at 7 a.m. (1200 GMT) in more than two dozen states.

Trump's campaign has suggested he may declare victory on election night even while millions of ballots have yet to be counted, just as he did four years ago. The former president has repeatedly said any defeat could only stem from widespread fraud, echoing his false claims from 2020. The winner may not be known for days if the margins in key states are as slim as expected.

No matter who wins the White House, history will be made.

Harris, 60, the first female vice president, would become the first woman, Black woman and South Asian American to win the presidency. Trump, 78, the only president to be impeached twice and the first former president to be criminally convicted, would also become the first president to win non-consecutive terms in more than a century.

Opinion polls in the campaign's final days have shown the candidates running neck-and-neck in each of the seven states likely to determine the winner: Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin.

Reuters/Ipsos polling shows a significant gender gap, with Harris leading among women by 12 percentage points and Trump winning among men by 7 percentage points.

The contest reflects a deeply polarized nation whose divisions have only grown starker during a fiercely competitive race. Trump has employed increasingly dark and apocalyptic rhetoric on the campaign trail. Harris has urged Americans to come together, while also warning that a second Trump term would threaten the very underpinnings of American democracy.

Control of both chambers of Congress is also up for grabs. Republicans have an easier path in the U.S. Senate, where Democrats are defending several seats in Republican-leaning states, while the House of Representatives looks like a toss-up.

The candidates spent the final weekend barnstorming the swing states in search of every available vote. Trump staged his final rally on Monday evening in Grand Rapids, Michigan, while Harris held twin rallies in Pittsburgh and Philadelphia.

More than 80 million Americans had already voted before Tuesday, either via mail or in person, according to the University of Florida Election Lab.