Two partygoers have been shot by police during a fancy-dress swingers ball at a Melbourne nightclub after what might have been a fake gun was pulled on officers.

A man and a woman sustained gunshot wounds at Inflation nightclub on King Street shortly after 3am on Saturday.

The club was hosting a Saints and Sinners Ball, an erotic fancy-dress party described on its website as a “no holds barred extravaganza of adult fun”.

Police arrived at the club after a report of a man being armed with a gun at the venue.

Fairfax Media reports the 35-year-old man was dressed as Batman character the Joker and was with a woman dressed as Harley Quinn.

The man allegedly drew a handgun from his pants and pointed it at approaching officers and would not drop it when asked.

“As a response police then fired a number of shots and a male and female were injured,” Superintendent Lisa Hardeman told reporters on Saturday morning, but wouldn’t comment on reports the man was also shot with a stun gun.

Security staff at the club told police they thought the gun might have been a fake.

Police could not yet confirm whether the firearm was real or an imitation but they said it was being investigated.

“When a firearm is pointed at you in these circumstances, police are not sure at that stage whether it is real or an imitation,” Hardeman said.

“That will be part of the investigation.”

The man was shot in the torso and taken to Royal Melbourne hospital under police guard in a critical condition.

The woman was shot in the leg and taken to the Alfred hospital in a stable condition.

The “rockers, punks and goths” themed ball was aimed at “broadminded adults” and tickets were sold at $55 each.