Democratic presidential hopefuls hit the streets as they faced a last chance to persuade the state's voters that they were the party's best bet to take on US President Donald Trump in November.
Recent state polls showed US Senator Bernie Sanders, a progressive from neighbouring Vermont, leading the crowded field.
He is followed by moderates former South Bend, Indiana, mayor Pete Buttigieg and US Senator Amy Klobuchar.
US Senator Elizabeth Warren of Massachusetts and former vice-president Joe Biden will also be angling for the support of voters who were expected to pack into schools, churches and city offices where ballots are cast.
New Hampshire is the second contest of the US presidential nominating cycle.
And while few votes are on offer, it gives candidates a chance to build momentum for their campaigns in a crowded field.
Mr Buttigieg's supporters greeted him at a Manchester school before dawn yesterday, waving their blue and yellow "Pete 2020" campaign signs as they chanted in support of "President Pete".
The 38-year-old military veteran shook hands and took selfies with the enthusiastic crowd.
Less than five minutes later he headed back to an SUV, a walk slowed by the throng of media cameras surrounding him.
"It feels good out here," he said, smiling as reporters asked how he thought he would fare in yesterday's primary.
Voter Sara Lutat (60) emerged from the school soon after, having cast her vote for Mr Buttigieg.
"I think he's the one who can beat Trump," she said, adding that he was grounded and had progressive ideas but nothing "too far out there".
"Actually, I don't care who wins as long as he's not in the White House," Ms Lutat said, referring to Mr Trump.
"I wish the Democratic Party would get it together.
"Otherwise, we're going to be stuck in limbo another four years. Frankly, it's too scary," she added.
Rebecca Balzano, a 38-year-old cook at a local restaurant, called Mr Buttigieg "too new, too young" and said she voted for Mr Sanders.
"Everything he says, I'm all for," she said.
"We need the Bern man in office."
Democratic voters in the state are faced with a lengthy ballot listing 33 names - including top-tier candidates, former hopefuls who have already dropped out of the race and some contenders who never attained a national profile.
One name not on the list is former New York City Mayor Michael Bloomberg, a late entrant to the race and who is skipping the first four contests.
That didn't stop voters in the mountain hamlet of Dixville Notch from picking the billionaire founder of the media company that bears his name as a write-in candidate when they voted just after midnight on Tuesday.
He won three of the five ballots cast.
Les Otten, a registered Republican who is redeveloping the ski lodge where the vote took place, said he voted for Mr Bloomberg because he is a moderate and his agenda addresses climate change and the ballooning federal budget deficit.
"I did what I had to do," Mr Otten said.
Earlier at his campaign rally in Manchester, New Hampshire, Mr Trump whipped up chants of "Lock her up" against House speaker Nancy Pelosi, pushed election fraud conspiracy theories, and again dismissed the significance of the coronavirus epidemic.
He also predictably denigrated the Democratic candidates who are running against him.
His dismissals came as a new poll from Reuters/Ipsos forecast the president losing the 2020 battle to Bernie Sanders, Michael Bloomberg and Joe Biden and drawing with Pete Buttigieg and Elizabeth Warren.
In addition to Vice-President Mike Pence and Ivanka Trump, the president's daughter and senior adviser, Republican Senators Lindsey Graham and Rand Paul, House Republican Whip Steve Scalise and New Hampshire Governor Chris Sununu were set to campaign on his behalf.