Former congressman Newt Gingrich is projected to have won the South Carolina Republican presidential primary, shaking up the party's campaign to find a candidate for this year's presidential election.

Several national news organizations said their exit surveys of voters leaving polling places projected a solid victory for Gingrich.

The polls closed at 7 p.m. and within an hour, preliminary vote tallies showed Gingrich winning with about 40 percent of the vote. His chief rival, former Massachusetts governor Mitt Romney, had about 28 percent.

Just a week ago, Romney was expected to win easily, but his campaign was hard hit by attacks over his wealth and his career as a venture capitalist. And in South Carolina, a southeastern state with many conservative voters, there were doubts that Romney was conservative enough.

And as Romney faltered, Gingrich surged in the polls after two well-received debate performances.

But it could be hours before the final votes are tallied.

Former Pennsylvania senator Rick Santorum was in third, with about 17 percent. Texas Congressman Ron Paul was in fourth, with 13 percent.

Gingrich's upset victory means that all three of the election events held so far have had different winners. Romney won the New Hampshire primary last week, and Santorum won the Iowa caucuses on January 3. As a result, the battle will continue to be hard fought in the next primary state – Florida. Republicans there will vote on January 31.