Democratic front-runner John Kerry surged ahead of his rivals with victories in five of seven states, as John Edwards captured his home state of South Carolina and made a strong showing in Oklahoma.

Democrats across the U.S. voted Tuesday for the candidate they believe can challenge George W. Bush in the presidential election next November.

When the ballots were counted, it was clear Massachusetts Senator John Kerry is on a roll -- with wins in Arizona, Delaware, North Dakota, New Mexico and the most delegate-rich state, Missouri.

"It's a huge night," Kerry told reporters. "I'm stunned by it."

The Senator from the South, John Edwards, was also declared a winner in his birth state South Carolina.

Battling laryngitis, the North Carolina Senator addressed a jubilant crowd of supporters at his South Carolina campaign headquarters.

"In our country, in our America everything is possible," he said to the cheers of his supporters.

Edwards had previously vowed he would quit the nomination race if he didn't win the state.

He also made a strong showing in Oklahoma, landing just behind retired army general Wesley Clark. The race was so close that no winner can be declared until the vote is certified next week.

Nevertheless, Clark was quick to claim victory.

"As an old soldier from Arkansas, I couldn't be prouder of your support in this first election I've ever won," an elated Clark told supporters in Oklahoma.

However, some see Clark's withdrawal from the race as inevitable.

"I do not think he is going to last much longer. I give him another week, two weeks, and then I think he's out of there," Democratic strategist Peter Fenn told CTV's Canada AM.

"And then the question is does it come down to a two-person race, or does Edwards have problems getting traction?"

Howard Dean, the front-runner in the race before Iowa and New Hampshire, appeared to be feeling the effects of campaign missteps and his now-notorious "I have a scream" concession.

Having already laid off staff and cut spending, the former Vermont Governor vowed to keep going.

"We're going to have a tough night tonight," Dean acknowledged as the ballots were counted.

Dean told supporters he is still looking forward to victories in Washington and Massachusetts, where he hopes to keep his campaign alive.

For Connecticut Sen. Joseph Lieberman, however, such hope is now lost. He pulled the plug on his campaign after posting another poor showing.

"I know the results are disappointing tonight," Lieberman said, putting a brave face on his announcement.
"I have decided tonight to end my quest for the presidency."

Ohio Representative Dennis Kucinich and social activist Al Sharpton are also running.

Tuesday's contests are said to be the toughest yet for the seven candidates hoping to win the party's national convention on July 26.

While only 12 per cent, or 269 of a total 2,162 delegates up for grabs, these states are seen as more of a national test for candidates than earlier votes in Iowa and New Hampshire.

Part of the reason is that the seven states are more diverse. For instance, South Carolina is the first southern state, and the first state with a large African-American population. Arizona and New Mexico are the first states to represent large Latino populations.

And Missouri, with its allocation of 74 of the 269 delegates up for grabs (the most from a single state) is considered the biggest prize. Historically, voters in the state have come out in favour of the winner in every 20th century presidential election exception for 1956.

Leading up to the vote, Kerry has been leading national polls with a strong showing against his Democratic rivals, as well as strong indications he could win the presidency.

Fenn said that while there are still many primaries to come, many voters sense that Kerry could win against Bush.

"The money is going to flow to Kerry now as frontrunner, as are the endorsements in the United States."

A USA Today/CNN/Gallup poll had Kerry defeating Bush 53 per cent to 46 per cent, giving the Massachusetts senator a lead outside the survey's margin of error. Even Edwards had a strong showing in the poll, edging out Bush with 49 per cent support.

The race turns next to Michigan and Washington state, with a combined delegate total of 204. Maine, Tennessee, Virginia, the District of Columbia, Nevada, Wisconsin, Hawaii, Idaho and Utah follow with their primaries and caucuses before the pivotal showdown on March 2.

That's when delegate-rich California, Georgia, New York and Ohio vote for their nominees.

Party leaders expect the nomination to be clear by March 9, when Florida, Louisiana, Mississippi and Texas vote -- long before the final elections in New Jersey and Montana on June 8.