Barack Obama easily won South Carolina's bitterly contested Democratic presidential primary with the aid of heavy black support on Saturday, dealing a setback to rival Hillary Clinton after a week of political brawling.
Obama, an Illinois senator who would be the first black US president, routed Clinton in the latest showdown in a back-and-forth fight for the right to represent the Democratic Party in November's presidential election.
John Edwards, a former North Carolina senator, finished third in a state he won during his failed 2004 race, casting fresh doubt on the future of his campaign.
With nearly all the votes counted, Obama had doubled Clinton's vote total, winning 55 per cent to her 27 per cent. Edwards had 18 per cent.
The win for Obama after two consecutive losses to Clinton, in New Hampshire and Nevada, gave him new momentum heading into Feb 5 "Super Tuesday" Democratic contests in 22 states. Obama won the first contest in Iowa.
"Tonight, the cynics who believed that what began in the snows of Iowa was just an illusion were told a different story by the good people of South Carolina," Obama told a wildly enthusiastic crowd in Columbia, the South Carolina capital.
"In nine short days, nearly half the nation will have the chance to join us in saying that we are tired of business-as-usual in Washington, we are hungry for change, and we are ready to believe again," he said.
Clinton called Obama to congratulate him and headed from South Carolina to Tennessee, a Feb. 5 state, as the results began to roll in.
"We now turn our attention to the millions of Americans who will make their voices heard in Florida and the 22 states as well as American Samoa who will vote on February 5th," Clinton said in a statement.
The high stakes in South Carolina fueled a week of angry accusations and increasingly personal jabs between the two candidates, capped by a volley of attacks on Obama from Clinton's husband, former President Bill Clinton, and questions about the role of race.
Exit polls showed Obama won four of every five black voters, who made up more than half of the primary electorate. He also won one-quarter of white votes, higher than many had predicted. Edwards and Clinton split the remaining white vote.
Bill Clinton's effect
Bill Clinton's aggressive attacks on Obama appeared to hurt his wife, exit polls showed. About six of every 10 primary voters said his campaigning was important to their votes, and Obama won 47 percent of those. Hillary Clinton won 38 percent.
Obama also won more than half of the voters who decided in the last 24 hours, the exit polls showed.
Edwards, the 2004 Democratic vice presidential nominee, had chastised his two rivals for their squabbling and portrayed himself as the grown-up in the contests, but he was beaten badly in the state of his birth.
Voting was heavy at some polling stations and record turnout of more than 400,000 cast ballots in the first Democratic primary in the South.
Clinton, once seen as the inevitable nominee and the leader in South Carolina polls until recently, left the state for two days during the week and headed to states with contests on Feb. 5, leaving her husband to carry the campaign load here.
All three candidates have portrayed themselves as the strongest leaders of a shaky economy. Clinton has hammered Obama for a lack of experience and highlighted her readiness to lead "from day one" in the White House.
The Republican presidential contenders, who held their primary in South Carolina last week, focused on Florida's Tuesday primary.
Arizona Sen. John McCain and former Massachusetts Gov. Mitt Romney are in a tight race in Florida, polls show, after splitting contests last week -- McCain won South Carolina and Romney won Michigan.
McCain won the backing of Florida Gov. Charlie Crist on Saturday and turned the debate back to the Iraq war, accusing Romney of backing a timetable to pull US troops out -- a charge Romney angrily denied.
Former New York Mayor Rudy Giuliani is desperately seeking a good showing that could get him back in the race. Giuliani, who once led the Republican field in national polls, has slipped after he essentially pulled out of the early voting states to concentrate on Florida.
(Additional reporting by Ellen Wulfhorst, Tim Gaynor, Deborah Charles, Jason Szep; Editing by Peter Cooney)