Democratic socialist Zohran Mamdani was elected as the youngest mayor of New York City in over a century, becoming the first Muslim and first South Asian in the role.

He based his campaign on a pledge to put working people first and tax the rich to pay for his policies.

Mamdani, a relatively unknown 34-year-old state assemblyman of Indian descent, declared victory against his stalwart opponents: Andrew Cuomo, the 67-year-old former governor of New York who ran as an independent, and Republican Curtis Sliwa, 71, founder of the Guardian Angels, a crime patrol group.

The older candidates had painted the millennial from Queens as being too inexperienced to run the nation's largest city, a key financial hub. Cuomo said Mamdani would "kill the city".

The race saw a clear generational and ideological split among voters. Cuomo and Sliwa courted support from older voters, while Mamdani, the front-runner, overwhelmingly appealed to the young.

His supporters were clear why they had voted for him.

"I feel like he had the best interests at heart for working people in New York City," Matthew Maher, 54, from Brooklyn, told China Daily after casting his vote. "I liked (his policies) of free buses, free groceries.

"The main problem right now in America is how old everybody else is," Maher said. "They are so old and they have such old ideas about how to make things work that are no longer (relevant), even the ones with the best intentions. He's young, he has new ideas."

Mamdani, a social media savvy candidate, campaigned on increasing the city's corporate tax rate to pay for his ideas, a rent freeze for 1 million rent stabilized tenants, free government subsidized grocery stores and the elimination of city bus fares.

His win came as an ABC News exit poll showed the cost of living was the most important issue among over half of the electorate.

He also pledged to create a free childcare program for all New York City children aged six weeks to five-years-old.

This year's highly anticipated mayoral race saw a massive voter turnout at the polls, including 735,000 early voters. By Tuesday evening, over 2 million New Yorkers had voted in the race, more than at any time since 1969, the City Board of Elections said.

Voter turnout was higher than the 1.1 million votes cast in the entire 2021 mayoral contest when Democratic incumbent Eric Adams beat Sliwa, the City Board of Elections said.

Adams abandoned his re-election campaign in September after facing corruption charges that were later dismissed by a federal judge.

The mayor-elect's win is a beacon of light for Democrats nationally, who have struggled to find a unified voice after their disastrous loss in the last presidential general election. It also comes ahead of the 2026 midterms.

Other elections nationwide on Tuesday included governors in New Jersey and Virginia, and a ballot on redrawing congressional maps in California.

In June's Democratic nomination race, Mamdani beat the odds and defeated Cuomo, a previously popular three-term Democratic governor, who was forced to resign due to a sex scandal in 2021.

Mamdani's campaign won praise and a phone call from former president Barack Obama. Former president Bill Clinton also heaped praise on him, but both stopped short of endorsing him.

He gained full-throated endorsements from Democratic Representative Alexandria Ocasio-Cortez and Senator Bernie Sanders.

But he was criticized by President Donald Trump, who publicly backed Cuomo on the eve of the election.