US Presidential Candidate Senator Bernie Sanders speaks at a campaign rally at Keene State College in Keene, New Hampshire on Sunday. Sanders and Pete Buttigieg locked horns in their fight for the US Democratic presidential nomination. Photo: AFP

Bernie Sanders won New Hampshire's high-stakes Democratic primary on Tuesday, according to US network projections, leaving rivals including party stalwart Joe Biden in his wake as he staked his claim to challenge US President Donald Trump in November.

Sanders, the flag-bearer for the party's progressive wing, had 26 percent of votes with most of the count complete in the northeastern state, where he routed Hillary Clinton in 2016.

"Let me take this opportunity to thank the people of New Hampshire for a great victory tonight," Sanders told cheering supporters after NBC and ABC called the result in his favor.

"This victory here is the beginning of the end for Donald Trump," the senator from neighboring Vermont added as raised the roof with his rallying cry for fairer taxes and health care reform. 

Indiana ex-mayor Pete Buttigieg finished in second place at 24 percent as he readied for the more difficult battlegrounds ahead.

"Now our campaign moves on to Nevada, to South Carolina, to communities across our country. And we will welcome new allies to our movement at every step," he said.

Midwestern moderate Amy Klobuchar maintained a late surge to place third on about 20 percent, while liberal Elizabeth Warren finished in fourth at about nine percent.

Trump weighed in, tweeting, "Bootedgeedge (Buttigieg) is doing pretty well tonight. Giving Crazy Bernie a run for his money. Very interesting!" Trump tweeted.

After months atop the pack, Biden had already conceded he expected to do badly in New Hampshire, as he did a week earlier in Iowa - and the former vice president's worst fears were beginning to materialize as he languished in fifth with just over eight percent. 

The performance will be a body blow to the 77-year-old Biden, who has failed to generate the fund-raising numbers or the enthusiasm levels of his rivals for the top spot on the Democratic ticket.

White House hopefuls had been seeking clarity in the Granite State after the first-in-the-nation Iowa count devolved into chaos, with Sanders and Buttigieg eventually emerging neck-and-neck.

For tech entrepreneur Andrew Yang and Colorado Senator Michael Bennet, that meant facing reality and bowing out after they failed to make an impact. 

Buttigieg's camp will be happy with a solid result that could provide voters on the fence with much-needed reassurance after he won narrowly in Iowa.