Trump beats Haley in her home state of South Carolina

Donald Trump easily defeated Nikki Haley in South Carolina's Republican contest on Saturday, extending his winning streak as he marches toward a third consecutive presidential nomination and a rematch with Democratic President Joe Biden.

The former president had been widely favoured to win the Southern state, despite his litany of criminal charges and Haley's status as a native of South Carolina who won two terms as governor.

The big win will bolster calls from Trump's allies that Haley, his last remaining challenger, should drop out of the race but Haley, who appeared to have outperformed expectations based on opinion polls, again defiantly insisted she would fight on at least through Super Tuesday on March 5, when Republicans in 15 states and one US territory will cast ballots.

Trump was leading 59.9 per cent to 39.4 per cent, a margin of 20.5 percentage points, with about 92 per cent of the expected vote tallied, according to Edison Research. Statewide opinion polls prior to Saturday had given Trump an average lead of 27.6 percentage points, according to the tracking website 538.

"Forty percent is not some tiny group," Haley said, referring to her approximate share of the vote on Saturday. "There are huge numbers of voters in our Republican primaries who are saying they want an alternative."

Trump has now dominated all five contests thus far - in Iowa, New Hampshire, Nevada, the US Virgin Islands and now Haley's home state - leaving her with no evident path to the Republican nomination.