Former Sex and the City star and candidate for governor of New York Cynthia Nixon (left) speaks to a fellow passenger on the 4 train in Brooklyn. (File photo)
Image: Joe Penney/Reuters

Cynthia Nixon, the Sex and the City actress campaigning to become New York's first female governor, has slumped further behind the Democratic incumbent just days before the primary, a new poll revealed on Monday.

Two-term governor Andrew Cuomo, 60, leads Nixon 63-22 percent, up from 60-29 percent in late July, according to the latest poll of likely Democratic primary voters.

Democrats go to the polls Thursday in New York's gubernatorial primary. Nixon is campaigning hard to Cuomo's left, energised by a string of other insurgent wins in Democratic primaries elsewhere in the United States.

Many of those victories went undetected by polling, but Siena College pollster Steven Greenberg insisted Monday that Cuomo "seems poised to overwhelm Nixon".

He leads in every demographic group and in every region of the state, including among voters under 35 years old and self-described liberals, and has a 48-point lead among women, according to the poll.

"While the Nixon campaign has talked about increased turnout among new, young and more progressive voters, it doesn't appear that that will help her," said Greenberg.

Nixon's campaign hit back, saying that US polls had time and again missed a "new electorate" who have traditionally sat out the primaries but who are now energised by opposition to Donald Trump's presidency.

"Andrew Cuomo knows this race is tighter than this poll suggests, or he wouldn't be spending half a million dollars a day against us," said campaign spokeswoman Lauren Hitt. "Given how much money he's spent, it's hardly shocking that Cuomo would have expanded his lead with the establishment voters these polls capture."

A New York State Democratic Party mailer over the weekend that implied Nixon was anti-Semitic, without basis, sparked a furious backlash and forced an apology, with Cuomo denying that he had any knowledge of it.

Nixon, who has Jewish children and went to synagogue to celebrate the Jewish New Year on Sunday, has accused Cuomo of orchestrating a smear campaign.