DES MOINES: Former Massachusetts governor Mitt Romney won the Iowa Republican presidential caucuses by a mere eight votes over former US senator Rick Santorum, a party official said on Wednesday.

Romney's razor-thin, eight-vote margin of victory came out of a total 122,255 votes cast on Tuesday, Iowa Republican Party Chairman Matt Strawn said.

Romney won 25 per cent of the vote, or 30,015 votes, in the first contest in the state-by-state battle for the Republican presidential nomination to face Democratic President Barack Obama on November 6.

The Republican candidates now head to the New Hampshire primary next Tuesday, where Romney holds a commanding lead in the polls.

Santorum vaulted from the back of the pack to emerge as the latest conservative contender in a Republican race that has been marked by volatility. Ron Paul, a US congressman from Texas with libertarian views and an antiwar stance, came in third place with about 21 per cent of the vote.

Romney is a favourite of the party's business wing, while Santorum appeared to be consolidating the state's large bloc of Christian conservatives.

Voters gathered in public meetings at hundreds of sites around Iowa such as schools, libraries and churches, listening to speeches touting the various candidates before casting their ballots.