New Yorkers have gone to the polls to elect a new mayor, with progressive Democrat Bill de Blasio tipped for a landslide victory to replace billionaire Michael Bloomberg.

The 52-year-old public advocate and his black formerly lesbian wife promise a new style in a city transformed by 12 years of tough love under Bloomberg, who is stepping down after a record three terms.

De Blasio’s campaign has left Republican rival Joe Lhota trailing in the dust, addressing the concerns of the economically vulnerable middle class and tapping into a far larger Democratic electorate.

He went into the election with an historic 41-point lead over Lhota in an NBC-Wall Street Journal poll, putting him on course to be the first Democrat elected mayor of the biggest US city since 1989.

De Blasio voted on Tuesday with wife Chirlane at the public library in his gentrified Brooklyn neighbourhood of Park Slope, accompanied by their teenage children Chiara and Dante.

The city of 8.3 million has six times as many Democrat voters yet David Dinkins was the last mayor to win the race in 1989.

If elected New York’s 109th mayor, de Blasio promises to raise taxes to fund universal pre-kindergarten education and after school programs, and build 200,000 affordable housing units.

He wants to reform the “stop and frisk” policy, which critics say unfairly targets black and Hispanic minorities, but which supporters say has driven down crime.

His family has featured prominently in his campaign, an effort to connect to ordinary people trying to make ends meet and a vastly diverse electorate with 33.3 per cent of New York white, 25.5 per cent black, 28.6 per cent Hispanic and 12.7 per cent Asian.

His campaign has raised concerns about the gulf between rich and poor in a city with more than 440,000 millionaires but where 21 per cent live in poverty on $US30,944 ($A32,600) a year for a family of four.