HuffPost New York features news from the city and bloggers, who will write about New York food, fashion, entertainment and more.
It launches with blog posts from the writer Nora Ephron, talking about the annual Shakespeare in the Park, which she calls "the greatest thing about living in New York".
It also features the famous former detective Frank Serpico, writing about the shooting of a black policeman by a white policeman.
Huffington Post founder Ariana Huffington says in a note to readers that partnerships with "more than a dozen local outlets" would keep the site up to date with the latest going on in the city.
These include the Gotham Gazette and the Brooklyn Rail.
She said: "And we will, of course, make our community a big part of the mix. As we move forward, we hope you'll help shape our coverage via our Eyes & Ears citizen reporting unit.
"We'll be asking you to share your favourite local spots, point out what isn't working in your neighbourhood -- and what is being done to make it a better place to live."
HuffPost New York is being edited by Dan Collins, a journalist and author of books on Rudy Giuliani and Ed Koch.
The launch comes ahead of New York's mayoral elections, where Michael Bloomberg will run for a third term.
The local rollout follows the Huffington Post securing $25m in funding from a Silicon Valley investment fund in December.
It said it would use part of that cash to expand its presence local. It has already launched a local version of the Huffington Post in Chicago.