Heidelberg detectives are appealing for public assistance following an armed robbery at a fast food outlet in Ivanhoe.

Investigators have been told a man entered the store on Upper Heidelberg Road around 5pm on Sunday.

He threatened the lone female attendant with a knife and stole cash from the till.

The man left the store and was last seen walking down Kenilworth Parade.

The offender is perceived to be Caucasian, 185cm tall, thin build and was wearing a Carlton Football Club jacket and hat and black track pants.

Detectives have released an image of the man they believe may be able to assist with their enquiries.

Anyone with any information about the incident or the identity of the robber is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au