Donald Trump and Bernie Sanders secure victory in New Hampshire

Republican Donald Trump and Democrat Bernie Sanders have coasted to victory on a wave of voter anger in the New Hampshire presidential nominating contest, thrashing traditional US politicians in a display of anti-establishment power.

Sweeping wins by Trump, a New York billionaire, and Sanders, a democratic socialist, on Tuesday testified to the sizeable share of American voters upset at US economic conditions and willing to send a shockwave to Washington in the November 8 presidential election.

New Hampshire's verdict sets up a tough fight for Republicans in South Carolina's February 20 primary and for Democrats there on February 27.

Ohio Governor John Kasich won a spirited fight for second in the Republican field in New Hampshire, with US Senator Ted Cruz of Texas, former Florida Governor Jeb Bush and US Senator Marco Rubio of Florida fighting for third place. All four are now headed to South Carolina.

For Trump, New Hampshire showed he has staying power and can take a punch after losing on February 1 to Cruz in the first nominating contest, the Iowa caucuses.

His win showed pundits were wrong to think he would quickly self-destruct based on his penchant for insults and imprecise plans for the presidency.

Democrat Hillary Clinton, the former US secretary of state and former US senator, now looks wounded, trailing Sanders by 60 per cent to 39 per cent based on 86 per cent of the returns.

The wife of former President Bill Clinton, Clinton barely won Iowa and now has been trounced in New Hampshire, where young voters liked Sanders' populist proposals to break up big banks and have the government pay for free college tuition.

"People have every right to be angry but they're also hungry, they're hungry for solutions," Clinton, 68, said after congratulating the 74-year-old Sanders.

"I will work harder than anyone to actually make the changes that make your lives better."

Clinton was headed to New York, headquarters for her campaign, to regroup with top aides and prepare for a Democratic debate on Thursday.