Photo: vicpolicenews

Detectives have been told a male offender rode a bike through the drive-thru window of a fast food restaurant on the corner of Somerville and Williamstown roads just after 1am on 4 August.

The offender forced open the window, produced a firearm and made demands for the attendant to hand over cash.

The staff member handed over a quantity of cash and the offender rode off on his bike, north on Williamstown Road.

No one was physically injured during the incident and the investigation is ongoing.

The offender is perceived to be Caucasian in appearance, aged between 40 and 60 and was wearing a dark hooded top with grey track pants.

Investigators have released CCTV and images of a man they believe may be able to assist with their enquiries.

Anyone with information to is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au.