He swept past his only rivals on the ballot, self-help author Marianne Williamson, who won 2 per cent, and Minnesota congressman Dean Phillips, who won 1.6 per cent, US news organisations said.

As the results came in, Biden was at a campaign event in California, as he turns his attention to the next steps in his fight for re-election.

“Now in 2024, the people of South Carolina have spoken again, and I have no doubt that you have set us on the path to winning the presidency again – and making Donald Trump a loser – again,” Biden said in a statement.

“The stakes in this election could not be higher. There are extreme and dangerous voices at work in the country – led by Donald Trump.”

Ecstatic scenes greeted Biden’s win at a watch party for local Democratic volunteers at the Nippitaty Distillery in North Charleston.

“It’s awesome,” said Biden activist Lauren Insinger. “All these months of hard work, it’s mounted to this.”

Volunteer Bria Major-Backman added that they would now focus on “getting the voters engaged” for November.

Biden had said he was counting on South Carolina to repeat the feat when it launched his bid for the White House in 2020 after a series of stumbles.

Despite South Carolina being likely to remain in Republican hands in November, as it has done since 1980, Biden also regards the southern state as important as a proving ground for his support among black voters.

A number of recent polls have however shown their support slipping, especially among young Black men, amid frustration that he has not addressed their priorities despite them backing him four years ago.

There were also concerns about turnout this time, with only a trickle of voters at polling stations visited by Agence France-Presse in the historic city of Charleston as many people apparently viewed his victory as a foregone conclusion.

Several voters said Biden’s record as president was mostly satisfactory, while admitting there was a lack of enthusiasm for his second term bid – but that they did not want to see Trump win.

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“It’s the lesser of two evils,” said Noelle Paris, 63. “It had to be Biden, just because you know, again, the most viable candidate in terms of chances. But strong candidate? Not so much in my opinion.”

But Biden has also been building on momentum after training a series of attacks on Trump, who faces multiple criminal cases and whom Biden brands a threat to democracy.

Other polls have showed him edging ahead of Trump or neck-and-neck, even if his personal approval ratings remain at low levels not seen by a sitting president for decades.

“I think he’s done the best he could,” said Annette Hamilton, 63, casting her vote at a church hall in North Charleston. Asked if Biden could win in November, she replied: “I pray to God he will.”

Biden also pointed to his victory in an unofficial primary in New Hampshire, despite the fact that he was not on the ballot and voters had to write him in.

Biden pushed for South Carolina, whose population is 23 per cent Black, to be at the front of the Democratic primary calendar this year, above New Hampshire, whose population is almost entirely white.