He said a fight was underway in part of the venue and men were swinging punches.
"There's at least a dozen guys, these two massive guys in particular."
He said some men were smashing each other in the face.
The customer said he heard three bangs.
"There was a guy three metres away from me with a black revolver ... Then I looked at him and he had this gun up in the air."
The witness said after a brief gap, he heard what sounded like another three bangs.
He said some of the dancers were "freaking out big time".
"Within five minutes there were heaps of cops."
Calendar Girls has not yet made any comment about the incident.
Detective Senior Sergeant Scott Armstrong said police were called to a disorder incident "inside a Karangahape Rd venue" at about 3.25am on Sunday.
Armstrong, of Auckland City Crime Squad, said many patrons were leaving the venue as police arrived.
"People present in the area also reported that they believed a firearm had been discharged inside the venue during the disorder," Armstrong said.
"Police did not locate a firearm at the time and at this stage we are not aware of anyone sustaining gunshot injuries."
A man aged 30 was arrested on Karangahape Rd outside the venue and given a written warning for disorderly behaviour, Armstrong said.
A St John ambulance spokeswoman said three ambulances were sent to the area at 3.34am.
Three people had moderate injuries. Another two with serious injuries were taken to Auckland City Hospital.
Police were today analysing CCTV footage and speaking with witnesses.
Armstrong said anybody with information could phone 105 and quote file number 201122/9607, or anonymously call Crimestoppers on 0800 555 111.
