Erie, United States — Millions of Americans voted Tuesday in a presidential election defined by drama and uncertainty, with Kamala Harris and Donald Trump awaiting the outcome of a desperately close and hugely consequential race.

The result -- perhaps coming overnight, or not for several days -- will either make Harris the first woman president in the country's history, or hand Trump a comeback that sends shock waves around the world.

Polls show Democratic vice president Harris, 60, and Republican former president Trump, 78, may be heading for a photo finish after a head-spinning campaign.

Harris made a late, dramatic entrance into the race when President Joe Biden dropped out in July, while Trump has ridden out two assassination attempts and a criminal conviction.

Tens of millions of voters were expected to cast their ballots Tuesday, on top of the 83 million who have already voted early, and both candidates put in a final word to try to sway the last undecided voters.

"We've got to get it done. Today is voting day, and people need to get out and be active," Harris, who had already voted by mail, told Atlanta station WVEE-FM.

She described her opponent as "full of vengeance. He's full of grievance. It's all about himself."

'If it's a fair election'

Trump voted in Florida near his Mar-a-Lago residence, saying he felt "very confident" and that he wanted to be "very inclusive."

But he aired concerns about the vote count -- heightening fears he will reject the result and cite fraud if he loses.

"If it's a fair election, I would be the first one to acknowledge it," he said.

Trump has said he would not seek election again in 2028, but he also recently has repeated baseless claims of election fraud while saying he should "never have left" the White House in 2021.

Across the country, voters lined up including in Black Mountain, North Carolina, where the voting station was a makeshift tent due to recent hurricane damage and 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.

"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 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, and by extension the ability for the new president to enact their agenda, 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 days if the results are close, 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, and extra security provided for election workers.

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.

'Momentum'

On Monday -- the last day of rallies -- Harris went all-in on must-win Pennsylvania, telling a huge crowd in Philadelphia: "Momentum is on our side."

Trump -- who would become the first convicted felon and oldest person to win the presidency -- cast himself as the only solution to a country in terminal decline and overrun by "savage" migrants.

"We can fix every single problem our country faces and lead America -- indeed, the world -- to new heights of glory," he told his closing rally in Grand Rapids, Michigan.

Harris hammered home her opposition to Trump-backed abortion bans in multiple states -- a vote-winning position with crucial women voters.

Trump's return to power would instantly fuel international instability, with US allies in Europe and NATO alarmed by his isolationist "America First" policies.

(Source: Gregory Walton, with Michael Mathes in Washington, for AFP)