Hillary Clinton is on her way to winning the West Virginia primary by a significant margin, but her victory is expected to have little impact on Barack Obama's delegate lead.
With 80 per cent of polls reporting, Clinton had 67 per cent support while Obama had 26 per cent.
"I am so grateful for the overwhelming vote of condidence," Clinton told cheering supporters in Charleston.
She added, "I am more determined than ever to carry on this campaign."
Clinton was widely expected to win Tuesday and Obama conceded defeat before the polls had even closed, preferring to focus his efforts on Republican presidential candidate John McCain.
"This is our chance to build a new majority of Democrats and independents and Republicans who know that four more years of George Bush just won't do," Obama said in Missouri.
"This is our moment to turn the page on the divisions and distractions that pass for politics in Washington."
While West Virginians voted in the primary, four more superdelegates declared their support for Obama.
"This race, I believe, is over," Richard Romer, a former Colorado governor and former Democratic National Committee chairman, told reporters on a conference call.
One of the other superdelegates who declared for Obama was Ray Nagin, mayor of hurricane-ravaged New Orleans.
Only Clinton can decide when to withdraw from the primary, but Romer added: "There is a time we need to end it and direct ourselves to the general election. I think that time is now."
Clinton and Obama met on the floor of the U.S. Senate on Tuesday morning, where they briefly shook hands and chatted.
West Virginia had 28 pledged delegates at stake, and Clinton was expected to win by a large margin, possibly 15 to 25 points. But by late Tuesday, it appeared she would win by around 30 points.
"I think Democrats across the country tomorrow will be asking themselves why Senator Obama -- with all of his money, with all of the great press, with voters being told he was the inevitable nominee -- why did Senator Obama lose West Virginia by 15 points or so?" Clinton spokesperson Howard Wolfson told NBC's "Today" show on Tuesday.
"What does it say about his candidacy at this date that he can't beat Senator Clinton in a key swing state?"
Obama is mixed-race, having a white mother and black father. He has strong support in the African-American community.
Both West Virginia and Kentucky, another state where Clinton is expected to do well next week, are heavy in white, blue-collar and older voters.
However, Democrats divide up delegates based on a proportional share of the vote. Even if Clinton wins by large margins, those states don't have enough delegates to allow her to substantially cut into Obama's lead.
Obama, a rookie Illinois senator, has the support of 1,865 delegates in primaries held since January. He needs 2,025 to secure his party's nomination.
Clinton, a New York senator, is behind with 1,697 delegates. She's also fallen behind among superdelegates, senior party officials who get an automatic right to vote at the convention and aren't obligated to support any candidate in particular.
The superdelegates speak up
Jennifer Duffy of the Cook Political Report told Â鶹´«Ã½net that since last Tuesday, more than 30 superdelegates have declared for Obama.
"It's a sign. After today, the trickle will become a steady stream," he said.
However, Clinton may feel she has a responsibility to her core constituencies -- especially women over 45 -- not to quit, according to John Zogby of Zogby International.
He said there are talks going on between the Obama and Clinton camps on a way to get Hillary out of the race.
Part of that could mean some type of financial deal, he said, noting that Clinton has put US$14 million of her own money into keeping her campaign afloat.
"The longer she stays in, the more she goes into debt," he said.
Duffy said the vitriol level has declined, and there is an emerging understanding that the general presidential election campaign has begun.
With files from The Associated Press
