The victims included three men, one of whom died, and one woman, a spokesman for the New York Police Department said.
The rapper known as T.I. was headlining a concert at the club in the Union Square area when the shooting occurred about 10 p.m.
The motive for the shootings was unclear, and no arrests had been made as of late Wednesday night.
“People were freaking out,” said Diana Zuluaga, 40, of Manhattan, who was on the balcony. She said the loud music covered the sound of the first gunshot but a second shot sent concertgoers running.
Paul Cantor, 34, of Manhattan, was in the back of the club, which he said was filled with about 1,000 people. He said his attention was drawn to a backstage fight that spilled onto the stage.
He described seeing a man falling backward like a boxer who had been hit by a hard punch. “There was a body that came across the stage, sort of with flailing arms,” he said.
He said a second fight — perhaps related to the first — then broke out on the club’s floor. About five seconds later, he said, he heard the shots.
Ayo Fagbemi, 21, a University of Pennsylvania student, said T.I.’s DJ was playing songs to warm up the crowd.
“I think T.I. was about to go on,” he said. “Right when he was about to go on, I heard two gunshots and right after there was a stampede. There were at least three rounds after, but after the second one was when people started running.”
Sagine Morency, 20, said she “got stomped on” and lost a sandal in the hasty exit.
T.I., whose given name is Clifford Harris, 35, is a multiplatinum rapper and actor from Atlanta. Since 2001, he has released nine studio albums and successfully crossed over into the pop realm, scoring two No. 1 singles on the Billboard chart: “Whatever You Like” and “Live Your Life,” featuring Rihanna.
The rapper’s life has been chronicled in recent years on the VH1 reality show “T.I. & Tiny: The Family Hustle.” He announced in February that his tenth album, “Dime Trap,” would be released by his own Grand Hustle label in partnership with Jay Z’s Roc Nation. T.I. is also an artist-owner of Jay’s music streaming service, Tidal.
In 2009, T.I. pleaded guilty to three federal weapons charges stemming from a 2007 sting operation in which the rapper was caught obtaining three machine guns and two silencers that had been purchased for him. He pleaded guilty and was sentenced to one year and one day in prison.
Along with performing more than 1,000 hours of community service as part of his sentence, he participated in the MTV reality series “T.I.’s Road to Redemption,” in which he stressed the danger of guns. (In 2010, he returned to prison after violating his probation.)
On Twitter, users posted photographs of a chaotic situation.
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