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

Donald Trump's 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.

Her pledge to ensure a peaceful handover stood in stark contrast with Republican four years ago to admit defeat against Joe Biden, culminating in the 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 to offer her congratulations, an aide said.

Trump sealed his 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 , 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.

Harris had also hoped for a surge in support from women, but exit polls gave her only an eight-point advantage among the demographic, nearly half what Joe Biden mustered four years ago.