Port Phillip Crime Investigation Unit detectives are investigating the circumstances surrounding an armed robbery at a jewellery store in St Kilda this morning.

Investigators have been told a man threatened the owner of the Acland Street store with a firearm and forced his way in through the front door just before 8.30am.

The offender then let his accomplice into the rear of the store before the pair accessed the safe and made off with what is believed to be a quantity of jewellery of significant value.

The men were wearing hoodies and had their faces covered.

One of the men was also described as having a beard and was wearing sunglasses.

The victim was not physically injured.