US Senator Bernie Sanders has won the New Hampshire presidential nominating contest after Hillary Clinton conceded, while US media is projecting billionaire businessman Donald Trump will win the Republican primary.
A win would see Mr Trump solidify his frontrunner status in the race to be the party’s White House nominee in 2016.
The reality television star’s non-traditional campaign has been marked by calls for the deportation of illegal immigrants and temporarily banning Muslims from entering the United States.
Senator Sanders, who describes himself as a democratic socialist, has called for eradicating income inequality, breaking up the big banks and providing free college tuition.
He had 59 per cent of the vote based on about 32 per cent counted, ahead of former secretary of state Mrs Clinton, who had 39 per cent, CNN said.
“Together we have sent the message that will echo from Wall Street to Washington, from Maine to California, and that is that the government of our great country belongs to all of the people and not just a handful of wealthy campaign contributors,” he said in his victory speech.
Mrs Clinton had for months been the frontrunner nationally, but a Reuters/Ipsos poll from February 2-5 showed the two now in a dead heat.
Mrs Clinton, 68, congratulated Mr Sanders, 74, in a speech to supporters. She defended her progressive stances and vowed to be the candidate who fixes problems and not just state them.
She appealed to African-American and Latino voters and acknowledged she had work to do winning over young voters.
“People have every right to be angry, but they’re also hungry, they’re hungry for solutions,” she said.
“I will work harder than anyone to actually make the changes that make your lives better.
“When we stand together, we win. Thank you, New Hampshire!” tweeted Senator Sanders, who is treated like a local hero in this state that borders Vermont, which he represents in the US Senate.
“You can be certain that our victory tonight will prompt a desperate response from the nation’s financial elite and the political establishment who want to stop our campaign to transform America,” he said in an email to supporters.
In a statement, Mrs Clinton’s campaign said she had called Mr Sanders to congratulate him.
Campaign manager Robby Mook said in a memo they had “split” the first two nominating contests — Iowa was last week — and said the Democratic nomination would “very likely” be decided in March.
“It will be very difficult, if not impossible, for a Democrat to win the nomination without strong levels of support among African-American and Hispanic voters,” Mr Mook wrote in a memo titled “March Matters”.
“The nomination will very likely be won in March, not February, and we believe that Hillary Clinton is well positioned to build a strong — potentially insurmountable — delegate lead next month.”
A logjam of Republican candidates were in a dead heat for second place, networks said, with MSNBC and ABC America calling it for John Kasich.
Nearly an hour after polls closed, Mr Trump was in first place with 34 per cent of the vote. Ohio Governor John Kasich, who staked the viability of his campaign on the New Hampshire outcome was in second place with 16 per cent, CNN said, based on an estimated 33 per cent of returns.
Former Florida Governor Jeb Bush, the son and brother of former presidents, had 12 per cent. Senator Ted Cruz of Texas, who won the Iowa caucus last week, had 12 per cent, and US Senator Marco Rubio of Florida had 10 per cent.
The presidential election is on November 8.