The Hells Angels are believed to be behind a spate of shootings using high-powered military weapons including targeting two Melbourne businesses owned by a member of the rival Comancheros.
Police say prohibited AK-47 machine guns or an M1 carbine were used in drive-by shootings at a Melbourne gym and a tattoo parlour early on Monday.
Two explosive devices were thrown inside the Hallam gym, which was peppered with bullets as was a Dandenong tattoo studio about 10km away.
Both businesses are owned by a member of the Comancheros, reportedly the head of the local chapter.
Acting Deputy Commissioner Stephen Fontana says he believes the Hells Angels are the aggressors in the latest incidents and other recent attacks.
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Police believe the latest incidents are related to recent shootings at Outlaw Motorcycle Gang premises in Clayton South and Dandenong where military-style weapons were used.
The clubhouse of new bikie gang Rock Machine in Clayton South was peppered with more than 70 bullets on September 14 and in August the Bandidos' Dandenong clubhouse was also sprayed with bullets.
Mr Fontana said he was concerned about retaliation between the gangs amid growing violence and tensions.
He said he feared an innocent bystander could be killed or injured.
"In terms of the recent shootings the Hells Angels have been the aggressors, in terms of the incident at Clayton South, at Rock Machine's and the Bandidos' clubhouse, the Hells Angels and their affiliates are responsible," he told reporters on Monday.
Mr Fontana said police were concerned about the number of shootings that have occurred since March.
"We are appealing to anyone that has knowledge of the people involved or where the weapons may be located ... to track down these firearms and the people responsible," he said.
Police evacuated an area around the Hallam gym for most of Monday before the scene was declared safe at 3.30pm (AEST).
In an unrelated incident, a 44-year-old Tullamarine man believed to have connections to the Comancheros gang admitted himself to hospital with a gunshot wound to the upper body on Sunday after a shooting in the Mornington Peninsula.
Victoria Police established Operation Resound in March to address a growing number of shooting incidents and concerns about escalating bikie violence.
