Polls in New York opened at 6am ET (11am GMT) and will close at 9pm ET (2am GMT).
A result is expected to be announced soon after polls close. In 2021 a winner was announced about ten minutes after voting ended.
However, polls have narrowed in the final days before voting, which may mean a result will be announced later this time.
Last month one poll gave Mamdani a 26-point lead.
However, the latest AtlasIntel poll, published on the eve of voting, showed Mamdani’s lead over Cuomo down to under five points.
Trump: I’ll deport Mamdani if he wins
Trump has also threatened to take over the city if Mamdani wins, as well as arrest and deport him.
Mamdani was born in Kampala, Uganda, to parents of Indian descent. He lived in Uganda until he was five then his family moved to South Africa. The family settled in New York when he was aged seven. Mamdani is a US citizen.
His middle name is Kwame, named after the Ghanaian leader Kwame Nkrumah, who was prime minister of the country when it gained independence from Britain in 1957.
• Read in full: Who is Zohran Mamdani? Democratic candidate in line to be NYC mayor
Trump threatens to withhold funds
On the eve of the election, President Trump threatened to withhold federal funds from New York if Mamdani wins.
In a Truth Social post, the US president said: “If communist candidate Zohran Mamdani wins the Election for Mayor of New York City, It is highly unlikely that I will be contributing Federal Funds, other than the very minimum as required, to my beloved first home.”
Trump told people to vote for Andrew Cuomo, an independent candidate
MARK SCHIEFELBEIN/AP
New York received about $7.4 billion (£5.6 billion) in federal funding this year.
In an interview with CBS News’s 60 Minutes programme, Trump said: “It’s going to be hard for me as the president to give a lot of money to New York. Because if you have a communist running New York, all you’re doing is wasting the money you’re sending there.”
Mamdani has denied he is a communist and called himself a democratic socialist. In one interview he described himself as “kind of like a Scandinavian politician”.
Trump urged New Yorkers to vote for Andrew Cuomo, even if they do not like the former governor.
World watches as New Yorkers head to polls
New York City’s voters are choosing who they want as the next mayor of America’s largest city — and the outcome is being keenly watched at home and abroad.
Zohran Mamdani, who won the Democratic primary this year, faces the former governor Andrew Cuomo, who is running as an independent, and the perennial Republican candidate Curtis Sliwa.
Zohran Mamdani at a campaign event in Queens on Saturday
STEPHANIE KEITH/GETTY IMAGES
A victory for Mamdani, 34, who led the polls coming into the vote, would give New York its first Muslim mayor and youngest leader in generations.
If Cuomo wins, he will have staged a remarkable political comeback four years after resigning as New York governor over a barrage of sexual harassment allegations.
Andrew Cuomo on the campaign trail on Monday
SETH WENIG/AP
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