Police are investigating an armed robbery at an Elsternwick jewellry store on Monday afternoon.

Investigators have been told two men, one armed with a sledgehammer and the other a handgun, entered the Riddell Parade store just after midday on 5 September.

Once inside the store, the pair have threatened staff and smashed glass cabinets, stealing a quantity of jewelry before fleeing.

The two offenders got into a waiting stolen grey 2011 Mitsubishi Outlander station wagon, driven by a third offender.

The car drove south on Riddell Parade, then east on Rowan Street where one of the occupants got out and into another vehicle, believed to be a silver 1998 Mercedes Coupe.

Both vehicles then left the area.

The Mitsubishi, registration YSF 086 was stolen during a daytime burglary in Diamond Creek on 31 August.

No shots were fired during the incident and two male and two female store attendants, aged in their 30s and 50s, were not physically injured.

The offenders are described as aged in their early 20s, thin build and Australian accents.

Both men had their faces covered with what appears to be t-shirts.