Barack Obama took a big step on Thursday toward becoming the first black US president when his campaign for change caught fire in Iowa and swept him past Hillary Clinton in the opening Democratic nominating contest.

Republican underdog Mike Huckabee capped a stunning political rise to beat rival Mitt Romney in Iowa, despite being dramatically outspent by the wealthy former Massachusetts governor and venture capitalist.

Obama, an Illinois senator, captured the first Democratic prize on the road to the White House with a comeback triumph over New York Sen. Clinton and former North Carolina Sen. John Edwards, who were in a tight battle for second.

"We are choosing hope over fear, we are choosing unity over division and sending a powerful message that change is coming to America," Obama told thousands of cheering, chanting and foot-stamping supporters.

Both Obama and Huckabee, a former Arkansas governor and ordained Baptist minister, once trailed better-known rivals Clinton and Romney in their race to be on the November election ballot.

But they rode a wave of grassroots enthusiasm to victories by touting an outsider's message of change in Washington.

"Tonight what we have seen is a new day in American politics," Huckabee, with actor and supporter Chuck Norris nearby, told cheering backers in Des Moines. "Tonight we proved that American politics is still in the hands of people like you."    

The 2008 campaign is the most open presidential race in more than 50 years, with no sitting president or vice president seeking their party's nomination, and the Iowa contest was the most hotly contested in the state's history.

Turnout among Democrats topped 220,000, smashing the previous record of 124,000 in 2004 -- testament to the high enthusiasm among Democrats heading into November's election.

For the winner in Iowa, the prize is valuable momentum and at least a temporary claim to the front-runner's slot in their battle to win the party's presidential nomination in the November election.

All eyes now turn to New Hampshire, which holds the next contest on Tuesday and where Romney and Clinton will face high-pressure bids to revive their candidacies.

The loss was a heavy blow for Clinton, the former first lady who a few months ago was considered in some quarters the almost certain Democratic nominee. She now faces immense pressure to turn around her campaign in New Hampshire over the next five days.

"Today we are sending a clear message that we are going to have change, and that change will be a Democratic president in the White House," Clinton, with husband and former President Bill Clinton at her shoulder, said in Des Moines.

Edwards, who at one time led polls in Iowa and finished a strong second here during a failed 2004 presidential bid, also faces questions about the viability of his candidacy as he goes forward.

The first casualties of the evening were Connecticut Sen. Chris Dodd and Delaware Sen. Joseph Biden, who both finished well out of the Democratic race and dropped out afterward. Dodd had moved his family to Iowa to concentrate on the campaign.

Obama's win effectively makes him the candidate to beat among Democrats, and a win next week in New Hampshire could put him in prime position to capture the nomination. After Nevada on Jan 19, the next big contest would be in South Carolina, where more than half of the voters in the Democratic primary are likely to be black.

Entrance polls showed Obama won big among young voters and even beat Clinton among women voters as his message of change resonated with voters.

Iowa voters filled gathering spots in more than 1,700 precincts around the state to declare a presidential preference in Iowa's caucuses, which open the state-by-state battle to choose candidates in the Nov. 4 election to succeed President George W Bush.

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