Americans vote: Who will win-Trump or Harris?

Election Day voting was underway till the filing of the report on Tuesday at 10pm after an extraordinary -- and for many unnerving -- US presidential race, report agencies.

Democratic Vice-President Kamala Harris and Republican Donald Trump, the former president, have been running neck-and-neck for weeks.

Whoever wins the US presidency is set to make history.

Harris would be the first woman, and Black and South Asian American to serve as commander-in-chief in the country's 248-year history.

While there is no question that Harris's candidacy is historic, she has deliberately downplayed the identity-focused aspects of her campaign, pitching herself as a candidate for "all Americans".

A Trump victory, meanwhile, would hold a different kind of historical significance.

The 78-year-old would become the first person convicted of a felony and elected to the US presidency, having been convicted of 34 felony counts in a New York hush-money case a little more than five months ago.

He would also be the first president to serve non-consecutive terms in more than 100 years.

Trump, who still faces felony charges in at least two separate criminal cases, argues he is the victim of a politicised justice system.

The first polls close at 18:00 EST (23:00 GMT) on Tuesday evening and the last at 01:00 EST (06:00 GMT) early on Wednesday.

In some presidential races the victor has been named late on election night, or early the next morning.

This time, the knife-edge race in many states could mean media outlets wait longer before projecting who has won.

Narrow victories could also mean recounts.

In the key swing state of Pennsylvania, for example, a recount would be required if there's a half-percentage-point difference between the votes cast for the winner and loser. In 2020, the margin was just over 1.1 percentage points.

The bitter rivals had spent their final day of the campaign frenetically working to get their supporters out to the polls and courting any last undecided voters in the swing states expected to decide the outcome.

But despite head-spinning twists in the campaign -- from Harris's dramatic entrance when President Joe Biden dropped out in July, to Trump riding out two assassination attempts and a criminal conviction -- nothing has broken the opinion poll deadlock.

Tens of millions of voters are expected to cast their ballots, on top of the 83 million who have already voted early.

Americans lined up before dawn including in Black Mountain, North Carolina, where the voting station was a makeshift tent erected after severe flooding.

Long queues also formed in Erie, a critical city in battleground Pennsylvania.

"It's way, way, way more people here than the last" election, Marchelle Beason, 46, told AFP after casting her ballot for Harris at an elementary school and putting on an "I voted" sticker.

"We're so divided right now, and she's about peace. And everything that her opponent has to say is really negative," she added.

At the same school, 56-year-old Darlene Taylor, who said she lives on disability benefits, noted her main issue is to "close the border."

"We don't need another four more years of high inflation, gas prices (and) lying," said Taylor, who wore a homemade Trump shirt.

Control of Congress is also at stake. All 435 seats in the House of Representatives are up for grabs, as are 34 of the Senate's 100 seats.

A final presidential outcome may not be known for several days if the results are as close as polls suggest, adding to tensions in a deeply divided nation.

And there are fears of turmoil and even violence if Trump loses, and then contests the result as he did in 2020. Barriers have been erected around the White House.

The world is anxiously watching, as the result will have major implications for conflicts in the Middle East, Russia's war in Ukraine, and tackling climate change, which Trump calls a hoax.

Harris and Trump are effectively tied in the seven main swing states. On Monday, Harris went all-in on must-win Pennsylvania, rallying on the Philadelphia steps made famous in the "Rocky" movie and declaring: "Momentum is on our side."

However "this could be one of the closest races in history -- every single vote matters," cautioned Harris.