Republican presidential candidate Newt Gingrich trounced frontrunner Mitt Romney in South Carolina on Saturday in a jarring victory that indicates the party's battle to pick a challenger to President Barack Obama may last months, not weeks.

Gingrich's come-from-behind triumph in the primary in the conservative southern state injects unexpected volatility into a Republican nominating race that until this week appeared to be a coronation for Romney, the former Massachusetts governor and private-equity chief.

Instead, voters in South Carolina rejected Romney's pitch that he is the best bet to fix a broken US economy and defeat Obama, a Democrat, in the November 6 election.

Three different candidates - Gingrich, Romney and former US senator Rick Santorum - now have won the first three contests in the state-by-state battle for the Republican presidential nomination to face Obama.

Gingrich's triumph may lead to a protracted battle of attrition as Republican candidates spend millions of dollars to tear each other down rather than uniting behind a standardbearer to take back the White House.     

With nearly all the votes counted, Gingrich had pulled in 40 percent of the vote, followed by Romney with 28 percent, networks reported. Santorum was in third with 17 percent and US congressman Ron Paul in fourth with 13 percent. The next contest is the Florida primary on Jan. 31.

Riding a series of feisty debate performances, the former speaker of the House of Representatives captured the lingering unease of conservative voters in South Carolina who view Romney's moderate past and shifting policy stances with suspicion. Gingrich argued that he would be able to better articulate the party's conservative ideals.

South Carolina was a stunning turnaround for Gingrich, whose campaign barely survived after top staff quit last June and stumbled to a disappointing finish just three weeks ago in Iowa, the first Republican nominating contest. He finished fourth in both Iowa and New Hampshire a week later as conservatives split their votes among several candidates.

Gingrich contrasted his sometimes-chaotic management style with Romney's buttoned-down approach, arguing that his campaign was powered by ideas rather than logistics. Romney is one of the wealthiest candidates ever to run for president and his campaign is well financed. - Reuters