Of the seven shot, two were from outside of New York City and the rest from Brooklyn, Shea said.
Shea said that among the victims, two were from "out of state" and the remaining five resided in different areas of Brooklyn.
Shea said there was "evidence of gambling" inside, including cards and dice.
Mickens said that when he headed toward the club after the shooting he saw people running and screaming, "Oh God!" Authorities declined to identify the victims but said the men killed ranged from 32 to 49 years old. He said that a preliminary investigation revealed that at least 15 shots were fired.
Chief of Patrol Rodney K. Harrison said there were never any complaints of a gambling operation at the location, which was only a few blocks away from the 77th precinct.
Police said that the shooting took place at 74 Utica Avenue, in the Weeksville neighbourhood of Brooklyn. When cops arrived, they found four men dead, two men shot in the leg and arm, respectively, and a woman shot in the leg.
A motive was not immediately clear, and no arrests have been made.
The shooting took place in a part of Brooklyn that has struggled with gang violence.
Mayor of New York City Bill de Blasio, in a message posted on Twitter, said the city "awoke to senseless gun violence".
Crime-scene tape surrounded the building Saturday morning and investigators in white jumpsuits could be seen going in and out.