While Biden, 81, faced little opposition, the vote was being closely watched amid concerns about his popularity, especially with Black voters.

Edison Research made the prediction soon after polls closed at 7pm local time on Saturday.

With about one-fifth of expected ballots counted, Biden won about 33,000 votes, or 97% of what has been tallied so far, way ahead of his two main challengers, US Representative Dean Phillips and best-selling self-help author Marianne Williamson.

In a victory statement, the Biden campaign said: “In 2020, it was the voters of South Carolina who proved the pundits wrong, breathed new life into our campaign, and set us on the path to winning the presidency.

“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,” the campaign said in a statement.

Four years ago, it was South Carolina’s Black vote in the state’s primary that helped ignite his campaign and ultimately propel him to the White House.

Biden, an unpopular incumbent who faces little competition for his party’s nomination in subsequent state primaries leading up to the Nov 5 US election, hoped for an overwhelming victory in South Carolina.

Besides campaign fears that South Carolina’s heavily Black electorate might not be energised this time around, there also were doubts about his age and concerns about high consumer prices and security along the US-Mexican border.

Democratic officials interviewed by Reuters expected somewhere between 100,000 and 200,000 total primary votes, after a county-by-county tour of the southern state aimed at exciting voters and multiple events featuring Biden or vice-president Kamala Harris.