US Republicans face first primary

The former governor of neighbouring Massachusetts carried a sizeable lead in polls into voting day, a sufficient cushion that should force rivals Ron Paul, Jon Huntsman, Newt Gingrich and Rick Santorum into a battle for second place.

Romney, 63, would be the first Republican who is not an incumbent president to win the first two early voting states, after his slim eight-vote victory over Rick Santorum a week ago in the Iowa caucuses.

A more resounding win on Tuesday would give him momentum going into South Carolina on 21 January and Florida on 31 January. He leads in both states and victories there could all but sew up his nomination to face Democratic President Barack Obama in the 6 November election.

It was unclear how much damage had been done by a mess of his own making in which Romney declared "I like being able to fire people," in addressing his desire for greater competition between health insurance companies.

His opponents, Republican and Democratic alike, quickly seized on the comment as evidence of an out-of-touch politician and coupled it with attacks over his record at Bain Capital, a firm that bought companies and restructured them.

In a remarkable turnaround in a party known for being friendly to business, Republicans seeking to slow Romney down sounded more like populists as they bashed Romney's work as a venture capitalist.

Gingrich, brooding over negative attacks from Romney and his backers that knocked him out of the front-runner position, has launched the toughest onslaught on Romney.

"Mitt Romney was not a capitalist during his reign at Bain. He was a predatory corporate raider," says a video produced by a pro-Gingrich group.

New Hampshire voting stations close at 7 pm EST (midnight GMT). About 250,000 people are expected to vote in the Republican primary while 75,000 are likely to vote to endorse Obama's re-election.