One man died and three other people were injured in the Wednesday night shooting at the Irving Plaza, where rapper T.I. was scheduled to perform.
The incident began as an argument that escalated into a fistfight outside a green room reserved for rappers on the bill at Wednesday night's concert, according to NYPD Chief of Detectives Robert Boyce.
After about five minutes of fisticuffs, someone pulled a gun and began shooting, he said.
Police have recovered five 9mm bullet casings, and are talking to witnesses and looking for video of the incident, he said.
Authorities do not yet know the motive for the argument or shooting, but say T.I. wasn't part of it.
"From what we can determine right now, he had nothing to do with this," Boyce said.
The man who died was 33, according to police.
Rapper Troy Ave -- whose real name is Roland Collins -- was shot in the leg and is expected to recover, Boyce said.
Another man, previously described as a 34-year-old, and a woman, said to be 26, were also shot and expected to survive.
Three other people were injured trying to escape the gunfire, Boyce said. Their injuries aren't serious, he said.
Video supposedly from inside Irving Plaza, located near Union Square, showed people frantically scrambling to leave the dance floor. Irving Plaza has a capacity of approximately 1,000 people.
It's unclear how guns made it inside the venue, where about 950 people were attending the concert, Boyce said.
The venue has metal detectors and a security staff, he added.
Irving Plaza posted a statement on its Facebook page saying "the safety of our guests is of the utmost importance" but referring all further comment to the New York City Police Department.
T.I. has not responded to CNN requests for comment.
The rapper was also set to perform at a separate venue, the 1 OAK nightclub, later in the evening, but authorities shut it down, according to law enforcement sources.
New York City Police Department Commissioner William Bratton told WOR radio Thursday that he believes police will likely be able to close the case soon, even though many people don't want to talk to investigators.
"When you talk about clowns, knuckleheads, it's unfortunate that still in the gangster rap world that that's what you're dealing with -- the gangster lifestyle if you will," Bratton said.