Zohran Mamdani's scored victory for the Democrats - making history as New York City's youngest mayor in a century.
The 34-year-old candidate focused his winning campaign on working-class issues.
It's a crushing defeat for the second-placed Trump-backed Independent Andrew Cuomo, and Republican Curtis Sliwa.
US correspondent Jonathan Kearsley says it's not gone down well with the US president.
"He's blaming some of the losses, not just in New York but in governing races in Virginia and New Jersey on the Government shutdown that's been going on for well over 30 days - and also on a lack of presence of himself."
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