The Independent Broad-based Anti-corruption Commission (IBAC) have announced they are investigating after police shot two partygoers at a Melbourne nightclub on the weekend.

A man and a woman were attending a fancy-dress swinger’s party at Inflation nightclub on Kings Street when they were struck by gunfire about 3am on Saturday.

The man, 35, suffered a gunshot wound to his chest, while the woman was struck in the leg.

IBAC Commissioner Stephen O’Bryan, QC, this afternoon said IBAC is now “reviewing” the incident, using information from nightclub staff, witnesses and CCTV.

“IBAC has confirmed with Victoria Police that arrangements are in place to deal with any potential or perceived conflicts of interest in the initial police investigation, including as a result of recent civil action (unrelated to the latest incident) taken by the owner of the nightclub,” Commissioner O’Bryan said in a statement.

“IBAC will oversight Victoria Police’s investigation being conducted by the Armed Crime Squad and Professional Standards.”

Police said they arrived at the club after a report of a man was armed with a gun at the venue.

Emergency services were called to the club about 3am. (9NEWS)

The man, dressed as Batman character the Joker, 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.

Police have not confirmed whether the firearm was real or an imitation but 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," Superintendent Hardeman said.

Inflation owner Martha Tsamis said the victim was not holding anything in his hand but instead was in a "compromising position" with the woman.

The official event flyer for the Ball. (Saints and Sinners Ball)

"Venue staff have stated that the male victim was not holding anything in his hand but rather he was in a compromising position with his female partner, which is a normal activity with the nature of this event," Ms Tsamis said in a Facebook post on Saturday.

"Security verified that a plastic toy accessory was displayed to, and passed by security and this information was given to police on arrival.

"No patron at the event came to us to inform our staff or security of this concern but apparently made an anonymous Triple Zero call to police."

The King Street club was hosting a "Saints and Sinners Ball". (9NEWS)

The "rockers, punks and goths" themed “Saints and Sinners” ball was aimed at "broadminded adults" and tickets sold for $55 per person.