Donald Trump claimed victory and pledged to "heal" the country Wednesday as results put him on the verge of beating Kamala Harris in a stunning White House comeback.

His exuberant speech came despite the fact that only Fox News had declared him the winner, with no other US networks having made the call so far.

As jubilant supporters cheered and chanted "USA," Trump took to the stage at his campaign headquarters in Florida along with his wife Melania and several of his children.

"We are going to help our country heal," the Republican former president said.

"It's a political victory that our country has never seen before."

US networks have called the swing states of Pennsylvania, Georgia and North Carolina for the 78-year-old, and he led the Democratic vice president in the others although they have not been called yet.

Gloom swiftly descended on Harris's camp.

"You won't hear from the vice president tonight but you will hear from her tomorrow," Cedric Richmond, Harris campaign co-chair, told a watch party in Washington as supporters left.

In a further blow to Democrats, Trump's Republican Party also seized control of the Senate, flipping two seats to overturn a narrow Democratic majority.

A Trump victory threatens to cause shockwaves around the world, as US allies in Europe and Asia fear a return of his nationalist policies and his praise of autocrats like Russia's Vladimir Putin.

But the US dollar surged and bitcoin hit a record high while most equity markets advanced as traders bet on a victory for Trump as the results rolled in.

Mood shift

Polls for weeks had shown a knife-edge race between Harris and Trump, who would be the oldest ever president at the time of inauguration, the first felon president and only the second in history to serve non-consecutive terms.

Trump also faces sentencing in a criminal case over hush money payments on November 26, while the controversy over his denial of his 2020 election defeat by Joe Biden still persists.

But in the end victory came surprisingly quickly.

The mood shifted sharply at Harris's watch party in Howard University -- her former college and a historically Black university in Washington -- as the results came in.

"I am scared," said Charlyn Anderson. "I am anxious now. I am leaving, my legs can barely move."

In contrast, the celebrations intensified at Trump's Mar-a-Lago resort in Florida and the watch party nearby.

Tech tycoon Elon Musk, who has backed Trump and stands to lead a government efficiency commission under him, posted a picture of himself with the Republican.

"Game, set and match," Musk said on X, the social media network he owns along with the Tesla electric vehicle firm and the Space X company.

Millions of Americans had lined up throughout Election Day -- and millions more voted early -- in a race with momentous consequences for the United States and the world.

They were deciding whether to either hand a historic comeback to Trump or make Harris the first woman in the world's most powerful job.

In a stark reminder of the tension -- and fears of outright violence -- dozens of bomb threats were made against polling stations in Georgia and Pennsylvania.

The FBI said the threats appeared to originate in Russia, which is accused by Washington of trying to meddle in the election. The threats were all hoaxes but succeeded in disrupting proceedings.

Dark rhetoric

Harris, 60, had aiming to be only the second Black and first person of South Asian descent to be president.

She made a dramatic entrance into the race when Biden dropped out in July, while Trump -- twice impeached while president -- has since ridden out two assassination attempts and a criminal conviction.

She hammered home her message that Trump was a threat to democracy and her opposition to Trump-backed abortion bans.

Trump has vowed an unprecedented deportation campaign of millions of undocumented immigrants, in a campaign full of dark rhetoric.

The election is being watched closely around the world including in the war zones of Ukraine and the Middle East. Trump has indicated he will cut aid to Kyiv's battle against the Russian invasion. (AFP)