Watch: Emotional moment Kamala Harris accepts defeat in US presidential election

Donald Trump's crushing presidential victory heralded a new era of uncertainty in the US and the world on Wednesday, as defeated Kamala Harris gave a defiant concession speech while vowing to help his transition to power.

An emotional Vice President Harris told tearful supporters in a speech in Washington to "not despair", urging them to "keep fighting" after her loss.

Stay up to date with the latest news. Follow KT on WhatsApp Channels.

Her pledge to ensure a peaceful handover stood in stark contrast with Republican Trump's unprecedented refusal four years ago to admit defeat against Joe Biden, culminating in the violent attack by his supporters on the US Capitol.

"While I concede this election, I do not concede the fight that fuelled this campaign," Harris said in her short, powerful speech at Howard University, her alma mater.

"I know many people feel like we are entering a dark time," she said, her voice hoarse as she made her first public remarks since Trump's surprisingly heavy victory. "But for the benefit of us all, I hope that's not the case."

Here's a video of her concession speech:

Harris — who had blasted Trump as a threat to democracy during her failed bid to become America's first woman president — earlier called him to offer her congratulations, an aide said.

Trump sealed his historic comeback to the White House overnight, cementing what is set to be more than a decade of US politics overshadowed by his hardline, disruptive right-wing politics.

The 78-year-old won wider margins than before, despite a criminal conviction, two impeachments while in office and warnings from his former chief of staff that he is a fascist.

Exit polls showed that voters' top concern remained the economy and inflation that spiked under Biden in the wake of the Covid pandemic.