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

With more than 75 percent of the precincts reporting, vote tallies showed Gingrich with about 40 percent of the vote. His chief rival, former Massachusetts Governor Mitt Romney, had about 27 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.

After the initial results emerged Saturday, Romney hit back, criticizing both President Obama and his Republican rivals.

“Our president has divided the nation, engaged in class warfare, and attacked the free enterprise system that has made America the economic envy of the world. We cannot defeat that president with a candidate who has joined in that very assault on free enterprise. (applause). When my opponents attack success and free enterprise, they are not only attacking me, they are attacking every person who dreams of a better future.”

In third in the South Carolina vote was former Pennsylvania senator Rick Santorum, with Texas Congressman Ron Paul in fourth. But it could be hours before the final votes are tallied.

Paul said he expects to get four to five times more votes in South Carolina this year than in the 2008 race. He said his cause of liberty is getting more attention now because of current conditions.

“Well the evidence has become clear that the efforts by government are failing, and we can't depend on the government to take care of us from cradle to grave, we can't depend on the government, on its efforts to promote, and to believe that we can police the world, and go in and nation-build, because we're all going broke.”

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.

Santorum made note of the volatility in his speech Saturday night.

“Well, three states, three winners, what a great country!”

The battle will continue to be hard fought in the next primary state – Florida. Republicans there will vote on January 31.