President Donald Trump has repeatedly described Mamdani as a "communist" and said on Monday that Hochul's endorsement was a "shocking development".

Hochul had withheld support for Mamdani - a self-proclaimed democratic socialist - for two months, and declined to endorse him after he stunned New York by defeating his main rival, former governor Andrew Cuomo, in the Democratic primary in June.

At the time, she noted misgivings about Mamdani's proposal to tax wealthy New Yorkers, arguing that it could lead to an exodus from the state.

"In the past few months, I've had frank conversations with him. We've had our disagreements," Hochul wrote in her opinion piece. "But in our conversations, I heard a leader who shares my commitment to a New York where children can grow up safe in their neighborhoods and where opportunity is within reach for every family."

"I heard a leader who is focused on making New York City affordable - a goal I enthusiastically support," she added.

While Mamdani already counts on the support of left-wing progressive politicians including New York Democratic representative Alexandria Ocasio Cortez and independent Vermont Senator Bernie Sanders, he has been at odds with the wider Democratic establishment - partly as a result of his strong support of Palestinians and harsh criticism of Israel.

"I've been glad to see him meet with Jewish leaders across the city, listening and addressing their concerns directly," Hochul added. "I look forward to working together to make sure New Yorkers of all faiths feel safe and welcome in New York City."

Polls showing Mamdani with a commanding lead over the other candidates -including Cuomo and incumbent Mayor Eric Adams - ahead of the city's election on 4 November.

In the editorial, Hochul took a thinly veiled swipe both at Cuomo - her former boss - and Adams, both of whom have been seen as becoming increasingly close to Trump. The US president has, in recent weeks, called on other candidates to rally behind Cuomo to defeat Mamdani.

"In light of the abhorrent and destructive policies coming out of Washington every day, I needed to know the next mayor will not be someone who would surrender one inch to President Trump," she said.

Despite Trump's public opposition to Mamdani's candidacy, late last week he said he believed that "it would look like he's going to win".

"And that's a rebellion," he told Fox. "It's also a rebellion against bad candidates."

Trump added that he is already thinking of ways in which he could impose some influence over Mamdani, whom he again referred to as "my little communist".

New York Governor Kathy Hochul endorses Zohran Mamdani for NYC mayor