Mitt Romney wins second U.S. primary.

The Sun News - Mitt Romney has won his second vote in the race to become the Republican US Presidential candidate.

The former Massachusetts governor got 39 per cent of the vote in the New Hampshire primary.

The decisive victory followed Romney's narrow win in last week's Iowa caucuses and he has now established himself as the man to beat for the nomination to challenge President Barack Obama.

His closest challenger Ron Paul put in a solid finish with 23 per cent. Jon Huntsman picked up 17 per cent.

And Romney immediately set his sights on Obama, telling supporters: "He has run out of ideas. Now, he's running out of excuses.

"And tonight, we are asking the good people of South Carolina to join the citizens of New Hampshire and make 2012 the year he runs out of time."

The crucial South Carolina primary is on January 21 followed by Florida on January 31.

After surviving a furious 11th-hour onslaught from his Republican rivals, who tarred him as a callous corporate raider who put people out of work, Romney defiantly trumpeted his business experience as his number-one asset.

"Make no mistake, in this campaign, I will offer the American ideals of economic freedom a clear and unapologetic defense," Romney said.

Latest results show Ron Paul came second in New Hampshire with 24 per cent, beating former Utah Governor Jon Huntsman (17%) into second place, with Newt Gingrich (11%) and Rick Santorum (10%) trailing.