The local police are also reportedly investigating whether a black Porsche SUV seen leaving the area is related to the shooting. The auto was later found burnt out.
Sunday's shooting took place around 3.20 a.m.in the lively entertainment district of Melbourne's southeastern suburb of Prahran, police said.
MELBOURNE SHOOTING: Evidence markers, identifying blood, line the path along Chapel St & Malvern Rd following a nightclub shooting.
"We just don't know if that's one of the four people that we've caught up with, or potentially whether there was somebody else who was injured", Mr Stamper said.
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Police said the men sustained "horrific injuries" outside the venue on Sunday morning.
Love Machine host Steve Yousif posted on Facebook: "Overwhelmed with all your calls and texts, nothing but love for you all".
People have been urged to avoid the area and that anyone with information or footage of the incident to contact Crime Stoppers on 1800 333 000.
Last year, a murder-suicide had left seven members of a family dead in Western Australia.
Gun violence is rare in Australia, which strengthened its gun laws following the murders of 35 people by a lone gunman in 1996 in Tasmania. Neighboring New Zealand has adopted legislation to ban semi-automatic firearms and assault rifles after its worst peacetime shooting in March, which killed 50 worshippers in two mosques in the city of Christchurch.