Police said four men were taken to hospital -- two in a critical condition -- after "multiple people were shot" outside the venue in the trendy inner-city suburb of Prahran early Sunday morning.
Three of the men were aged between 29 and 50, with the age of the fourth yet to be determined, police said.
A police spokeswoman told AFP the shooting was not believed to be linked to terrorism.
Police were expected to provide updates later Sunday.
The latest incident came after a spate of shootings in Melbourne in March that left five people dead in four separate incidents. Two of the incidents were believed to be gang-related.
Mass shootings are rare in Australia, which has strict firearms laws introduced in 1996 after 35 people were killed by a gunman in Port Arthur.
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