About 15 people were fighting when police arrived at RAIN on Water Street behind Cedar Lane, Police Chief Glenn O'Reilly said.
"As officers were breaking up the fight, several gun shots were fired," he said.
"One person was hit and transported to Hackensack University Medical Center," the chief said.
A resident who lives nearby reported hearing "two, maybe three" shots. It wasn't immediately clear whether the victim was a participant or a bystander.
The injury "does not appear to be life threatening at this time," O'Reilly said.
The Bergen County Sheriff's Bureau of Criminal Identification collected evidence.
An investigation was continuing.
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