Newt Gingrich has been tipped to win the crucial South Carolina Republican primary, according projections in the US media.

Fox News has predicted the victory of the former House speaker even as counting is progressing in the closely-fought primary. Mitt Romney will be placed second while Ron Paul and Rick Santorum are engaged in a battle to grab the third slot, Fox News says.

The results of the exit polls conducted by MSNBC and NBC also predicted the victory of Gingrich.

Gingrich dominated the two debates in South Carolina this week with a solid performance.

The winner in South Carolina has bagged the presidential nomination in each election since 1980, experts point out.