Former Massachusetts governor Mitt Romney has won the Republican primary in Michigan, giving his campaign for the US presidential nomination a big boost despite second-place finishes in two earlier contests.

Mr Romney needed the victory in Michigan, where he was born and where his father was once a popular governor, to be competitive in the February 5 Super Tuesday contests, when nearly half the US states choose Democratic and Republican candidates for the presidency.

Polls had shown Mr Romney, a former Massachusetts governor who grew up in Michigan in a famous political family, running even with Arizona Senator John McCain in a state where the ailing economy tops the agenda.

Mr Romney, who has spent millions of his own money in the race, needed a breakthrough win in Michigan where his father was a senior auto executive and popular governor in the 1960s to keep his White House hopes alive after second-place finishes in Iowa and New Hampshire.

A McCain win after last week's New Hampshire victory would have thrust him into the front-runner's role heading into contests in South Carolina and Florida.

Democrats also held a primary in Michigan but a dispute over the date of the vote led the national party to strip the state of its delegates to this summer's presidential nominating convention.

As a result, Mr Obama and Mr Edwards kept their names off the ballot and Ms Clinton was the only top contender listed. None of the top Democrats have campaigned in the state since the dispute arose.

The Republican vote was being counted in Michigan as Democratic White House contenders Barack Obama, Hillary Clinton and John Edwards prepared for an evening debate in Nevada - site of the party's next contest at the weekend.

The hectic schedule reflects the heightened intensity of the wide-open US presidential race, as both parties choose candidates for the November election to succeed President George W Bush.