Paramedics treated a further three people for minor injuries before two were taken to Canterbury Hospital.
Sixteen people at the scene had minor injuries. Of those, two men were taken to Royal Prince Alfred Hospital for treatment.
Multiple vehicles, including a police car, were damaged after reportedly being shot at.
Locals said the shooter was believed to be on the roof of a restaurant, and fired multiple shots on to the street.
About 9.30pm, police entered a unit above a business on Georges River Rd where several firearms were seized and a man was arrested.
The public was urged to “stay inside” as the police operation unfolded.
The suspect was taken to hospital under police guard for injuries suffered during the arrest, police said.
There have been no reports of police being injured.
Police have established a crime scene and inquiries into the shooting have commenced.
Road closures will remain in place for some time and motorists are advised to use alternative routes.
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