Billionaire Republican Donald Trump and Democrat Bernie Sanders were expected to defeat their mainstream rivals in the New Hampshire primary elections, giving them a much-needed boost as they chase their parties' nominations to contest the 2016 US presidential election.
On Tuesday, in an election year when Americans seem angry at traditional politicians, the two men held strong leads in polls over their respective opponents, as voters flocked to polling stations in New Hampshire.
A RealClearPolitics poll average shows Sanders - who has called for nothing short of a "political revolution" - leading 53.3 percent to 40.5 percent in the state, over Democratic frontrunner Hillary Clinton.
Trump soars ahead in the Republican camp on 31.2 percent - with no other candidate above 15 percent.
New Hampshire is the second state in the process of picking party nominees for the November 8 election to replace President Barack Obama.
"For the next few hours, the only thing you will hear is these two results," said Al Jazeera's Alan Fisher, reporting from New Hampshire.
"Here, most [voters] don't make up their minds until they're in the booth. On the Democrat side, Sanders has a big lead over Clinton. It's thought he would win. On the Republican side, Trump has a lead as well."
READ MORE: New Hampshire, the little state with the big voice
Independents make up about 43 percent of the New Hampshire electorate, while Democrats and Republicans make up about 30 percent each.
After a strong third-place showing in last week's Iowa caucuses, the first state to hold a nominating contest, Republican Marco Rubio needs another top-tier finish in New Hampshire to buttress his argument that he is the candidate around whom the party's leadership and wealthy donors should rally.
A debate performance by Rubio on Saturday night was widely mocked by Republicans and Democrats, as well as legions on social media, but a robust finish in New Hampshire may help defuse the notion that it did lasting damage.
Obama, who has not yet endorsed a Democratic candidate, expressed surprise at the leads in polls held by Trump and Sanders.
"Early on, often times, voters want to just vent and vote their passions," he told CBS News in an interview that aired on Tuesday.
READ MORE: Five things to watch in New Hampshire
Voting in New Hampshire, the first presidential primary of the 2016 US election cycle, began at midnight on Tuesday.
Nine registered voters in a tiny northern US community of Dixville Notch cast the first ballots, hours before most of the state.
That vote went 3-2 to John Kasich over Donald Trump for the Republicans, and 4-0 for Bernie Sanders over Hillary Rodham Clinton for the Democrats, the Washington Times reported.
That result is sometimes treated as a predictor of how the rest of the state will vote.
Voting will conclude by 8pm local time on Wednesday (0100 GMT Thursday).
Source: Al Jazeera and agencies