US presidential hopeful Barack Obama has secured a decisive win in the South Carolina primary election, as he bids to be the Democratic Party's candidate.
The Illinois senator beat his main rival, Hillary Clinton by 55% to 27%, with John Edwards third on 18%.
The result is a boost for Mr Obama's campaign ahead of Super Tuesday on 5 February, when 24 states vote for who they want to run for US president.
Republicans are campaigning for their next primary, in Florida on Tuesday.
Smiling broadly as he greeted supporters at a victory rally in the state capital, Columbia, Mr Obama delivered a rousing message of unity and hope.
"The choice in this election is not about regions or religions or genders," he said. "It's not about rich versus poor, young versus old and it is not about black versus white.
"This election is about the past versus the future."
Mr Obama referred to his win in the first contest, the Iowa caucuses, saying that the faith Democratic voters had shown in him then had been borne out in the result in South Carolina.
"Tonight the cynics who believed that what began in the snows of Iowa was an illusion were told a different story. "
Looking forward to Super Tuesday, he went on: "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."
Stressing his differences from the candidates representing the "status quo in Washington", he appeared to criticise the Clinton campaign for using divisive tactics.
"It's a status quo that extends beyond a particular party, and that status quo is fighting back with everything it's got, with the same old tactics that divide and distract us from solving the problems people face," he said.
Key to Mr Obama's victory was the support of African-American voters, who made up about half the electorate and four-fifths of whom supported him, according to exit poll data. About 17% supported Mrs Clinton.
Mr Obama also won about a quarter of the white vote, compared to just under 40% each for Mrs Clinton and Mr Edwards.
Mrs Clinton's campaign issued a statement saying she had called to congratulate Mr Obama and wish him well.
Mrs Clinton, who was on her way to Nashville, Tennessee, before the votes were counted, told a rally: "Now the eyes of the country turn to Tennessee and the other states voting on 5 February."
The primaries would mean "millions and millions of Americans are going to have their voices heard", she added.
Former President Bill Clinton, who has been campaigning on behalf of his wife, told a rally in Missouri that Mr Obama had "won fair and square".
Voting in South Carolina was brisk, producing a record turn-out of more than 530,000. By comparison, the turn-out for the 2004 Democratic primary was 280,000.
The BBC's Jamie Coomarasamy in South Carolina says the result gives an important lift to Mr Obama's campaign after consecutive defeats by Mrs Clinton in New Hampshire and Nevada.
Candidate wins nomination by accumulating 2,025 delegates
Most are "pledged delegates", won at primaries or caucuses
Delegates vote at summer convention to confirm nominee
It also sets the stage for a fierce battle between the two front-runners on Super Tuesday, he adds.
The fact that Mrs Clinton spent part of the week campaigning outside South Carolina signalled that she was not expecting to win there, correspondents say.
Mr Edwards, a native of South Carolina who won there in his failed run for the presidential nomination in 2004, has failed to improve on his second place to Mr Obama in Iowa at the start of January.
Correspondents say both parties' contests for the presidential nomination are so close that they could continue for weeks after Super Tuesday this year.
Once the candidate for each party has been selected, they will compete head-to-head to win the presidential election in November.