The gunfire erupted at the door of Slick's Go Go Bar on Nye Avenue just after 12:30 a.m. Wednesday.
Police say a dispute with a bouncer at the front door sparked the shooting, which killed the bouncer and the son of the club's owner. A third person, possibly a friend of the gunman, may have been caught in the crossfire.
''It appears the gunman was trying to enter the bar armed and was stopped by the bouncer," said Chief Anthony Ambrose of the Essex County Prosecutor's Office.
Two of the dead have been identified. They are Pierre Clervoyant, 34, of Elizabeth and Woodley Daniel, 32, of Irvington.
Two other people were shot, a 27 year old male from Irvington and a 34 year old male from East Orange, and were taken to University Hospital.
Witnesses said about 100 people were in the club at the time. The witnesess heard 7 to 15 shots fired right after some fighting on the steps of the club.
Police say one man fled the scene in a grey vehicle. So far there have been no arrests.
The Essex County Sheriff's Crimestoppers Program is offering up to $10,000 for information leading to the arrest and conviction of the suspect.