Rick Santorum has won Louisiana's Republican primary, but he still trails Mitt Romney by a wide margin in the national delegate count for the party nomination to challenge Barack Obama in November's presidential election.

With virtually all votes counted on Saturday, Santorum had 49 per cent of the vote, Romney 27 per cent, Newt Gingrich had 16 per cent, while Ron Paul had six per cent.

If those totals hold, Santorum and Romney would both gain delegates from Louisiana.

Santorum, a former senator from Pennsylvania, has picked up wins in a string of southern states and has emerged as the standard bearer of his party's conservative right, thwarting former Massachussetts governor Romney's efforts to wrap up the nomination before August's national party convention.

"The people of Louisiana sent a loud and clear message - this race is far from over," Santorum said in Green Bay, Wisconsin, where he watched the election results after making a series of campaign stops.

Saturday's primary allocated only 20 of Louisiana's 46 total Republican delegates, with the rest of the delegates set to be allocated at the state party convention in June.