Police are hunting for a man they believe has held up at least four stores at gunpoint in Maribyrnong and Braybrook.
In the latest incident a man entered a service station on Williamsons Road, Maribyrnong about 10.15pm on November 27, pulling out a gun and demanding cash before escaping on a bicycle.
Investigators believe the same man robbed a restaurant on Ashley Street, Braybrook about 8.40pm on November 24, drawing a gun and threatening staff before stealing cash and fleeing on a bicycle.
Acting Sergeant Alistair Parsons said police suspect the two incidents are related to two other recent armed robberies in Maribyrnong in which a man also produced a gun.
The first was about 9.10pm on September 30 at a service station on Hampstead Road, the second at a pharmacy on Hampstead Road shortly before 9pm on October 17.
Detectives have released CCTV vision of a man they believe can assist with their enquiries.
The man is described as Caucasian in appearance, between 20 and 30 years old, and about 170-180cm tall.
Anyone who recognises the man or has information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au