Donald Trump won a sweeping victory in the US presidential election on Wednesday, defeating Kamala Harris in a stunning political comeback that sent shock waves across the world.

The polarizing Republican's win, following one of the most hostile campaigns in modern US history, was all the more remarkable given an unprecedented criminal conviction, a near-miss assassination attempt, and warnings from a former chief of staff that he is a "fascist."

"It's a political victory that our country has never seen before," Trump told a victory party in Florida.

As supporters chanted "USA!", the 78-year-old added that his "magnificent" win would "allow us to make America great again."

World leaders swiftly pledged to work with Trump, led by Israel and Ukraine where the course of raging conflicts could depend on the new president and his isolationist "America First" foreign policy.

Vice President Harris, who only entered the race in July after President Joe Biden dropped out, ran a centrist campaign that highlighted Trump's inflammatory messaging and use of openly racist and sexist tropes.

But his apocalyptic warnings about immigration and championing of isolationism found their mark with voters battered by the post-Covid economy and eager for a change from the Biden years.

The campaign pointed to a nail-bitingly close contest, but the results came surprisingly fast, delivering a crushing victory that included wins in the swing states of Georgia, North Carolina, Pennsylvania and Wisconsin.

Gloom descended on her campaign and Harris cut short a planned watch party and canceled a speech. She is now due to speak later Wednesday.

- Change and turmoil -

Trump is the first president in more than a century to win a non-consecutive second term.

He is also the only person to be elected as a convicted felon -- he will face sentencing in a New York court for fraud on November 26.

Trump is on course to break another record as the oldest-ever sitting president during his four-year term. He will surpass Biden who is set to step down in January at the age of 82.

The dollar surged, stocks rallied and bitcoin struck a record high Wednesday as news of his victory emerged.

But turmoil likely lies ahead.

Trump's victory comes with a promise of radical policy shifts -- not just at home but also abroad.

He has repeatedly suggested he would end the conflict in Ukraine by pressuring Kyiv to cede land to Russia, and his threat of mass deportations of illegal immigrants has stirred deep concern in Latin America.

He also returns to the White House as a climate change denier, poised to dismantle his predecessor Biden's green policies and jeopardize global efforts to curb human-caused warming.

Even before Trump's victory was fully confirmed, foreign leaders rushed to send congratulations.

These included longtime Trump allies, Israeli Prime Minister Benjamin Netanyahu, Indian Prime Minister Narendra Modi and Turkish Prime Minister Recep Tayyip Erdogan.

Also messaging Trump was Ukrainian President Volodymyr Zelensky, who is predicted to see a rapid reduction in US military aid once Biden leaves office.

Zelensky said he hoped Trump's "impressive victory" would help his country find a "just peace."

The Kremlin said Russian President Vladimir Putin, on whom Trump has often lavished praise, did not plan to congratulate him.

NATO's chief, Mark Rutte, said Trump, who has frequently expressed displeasure with the US-led alliance, would make it "strong." 

- Showman's instinct -

For all his dark promises of political revenge against enemies at home and his criticisms of allies overseas, Trump remains famously unpredictable when it comes to matching words with actions.

His campaign rallies, filled with grievance, insults and misinformation, featured extreme rhetoric.

But he won positive coverage with viral online moments that played on his everyman appeal and his showman's instinct -- like his appearance at a McDonald's drive-thru and impromptu news conference from a garbage truck.

Star supporters like tech baron Elon Musk helped appeal to young men.

He campaigned on tax cuts, less regulation and the most significant increase in import tariffs in nearly a century to promote growth and boost manufacturing, despite warnings of trade wars and higher prices for US consumers.

Trump often lurched into foul language and violent imagery. But that hard-charging style played well with his unfailingly loyal base, which sees him as a Washington outsider.

When Harris joined the race in July, replacing Biden, she soon closed the yawning gap Trump had in opinion polls.

Her message of unity, focus on abortion rights and warnings of the threat Trump posed to democracy appeared to resonate, evidenced by a huge surge in fundraising. 

Ultimately, however, she fell short of what would have been a historic win as the first woman elected to the White House.