COLUMBIA (AFP) -- Former Republican House speaker Newt Gingrich decisively won a keenly-watched South Carolina Republican presidential primary Saturday with 40.4 percent of the vote, according to nearly complete official returns.

With 99.5 percent of the precincts reporting, the returns showed that former Massachusetts governor Mitt Romney was second with 27.9 percent of the ballot.

Rick Santorum, a former senator from Pennsylvania, was in third place with 17 percent of the vote, while Texas Congressman Ron Paul was fourth with 13 percent.

On top of the four Republican presidential candidates, 1.1 percent of the South Carolina vote went to black businessman Herman Cain, who has already dropped out of the race, but remained registered for the South Carolina primary.

A further 0.7 percent of the vote went to other candidates.   Republicans have yet to coalesce around a single candidate.

The first vote in Iowa on January 3 was eventually ruled to have been won by Santorum, although Romney, who took the second vote in New Hampshire, was initially believed to have triumphed.

Romney has the money and the on-the-ground organization, but suspicions linger over his Mormon faith and whether he is conservative enough.