Shots were fired outside Fitzy's Hotel in Loganholme, south of Brisbane, just after 8pm on Saturday, when a boxing meet for Logan City Titles was taking place.
A 19-year-old woman was taken to hospital, where she remains in a critical condition.
Three men, aged 27, 37 and 38, are also recovering in hospital in serious but stable conditions.
Police said the vehicle involved was seen leaving the scene.
A major police response was seen outside the venue on Saturday night and into the early hours of Sunday.
Bullet holes were visible on the outside of the building, while there were reports of a burnt-out car being found about 12km from the scene.
Logan City Titles said they were heartbroken and "praying for full recoveries" for those injured in the shooting.
"As a team, we are working through it and dealing with the emotions that come with this," the event organisers said in a statement on Sunday.
"Right now our thoughts go out to the victims and all that were affected."
The community was on high alert following the incident, locals said.
"We've never seen anything like this in Logan," mayor Jon Raven said in a social media post on Sunday.
"Everyone there will be processing trauma, especially the kids.
"If you know someone who was (at) Fitzy's last night, please wrap your arms around them and make sure they know the community is thinking of them."
Police said there was not believed to be any ongoing threat to the public.
Anyone with information about the incident is urged to contact police as the search for the shooter continues.
Police will address the media later on Sunday.
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