Barack Obama was given a comfortable lead by opinion polls ahead of Hillary Clinton, with John Edwards third.

This is the final contest for the Democrats before Super Tuesday in 10 days' time, when more than 20 states will vote in primary contests.

Republicans are campaigning for their next contest in Florida on Tuesday.

In a televised debate at the start of this week, Hillary Clinton and Barack Obama, clashed over their records, with what the BBC's Kevin Connolly says was a touch of real nastiness.

Mr Obama accused Mrs Clinton of saying anything to get elected, after earlier accusing her husband Bill Clinton of making false statements about him.

For her part, Mrs Clinton told Mr Obama it was hard to debate with someone who never took responsibility for any vote he cast.

Our correspondent says there seems little doubt that Mr Obama will win.

Around half of the registered Democrats in South Carolina are African-Americans, and most are expected to support him.

On Thursday, the New York Times formally endorsed Mrs Clinton as its preferred Democratic candidate for the White House.

It said it was hugely impressed by Mrs Clinton's knowledge, the force of her intellect and her experience.

"The idea of the first African-American nominee of a major party also is exhilarating, and so is the prospect of the first woman nominee," it said in an editorial. "'Firstness' is not a reason to choose."

'Thin-skinned'

A win by a comfortable margin for Mr Obama would help dull the memory of Mrs Clinton's recent victories in primaries in New Hampshire and Nevada. Mrs Clinton has spent part of the week campaigning elsewhere signalling that she is not expecting to win.

In her absence her husband loomed larger in the campaign, attacking Mr Obama as thin-skinned and inexperienced.

The third candidate John Edwards won South Carolina in his failed run for the presidential nomination in 2004 but he has no real chance of winning his time.

This, our correspondent says, raises further doubts about how long he will stay in the race.