The armed robbery took place about 4.15am on Monday morning, November 23, at the BP service station on Yass Road.

CCTV footage showed a man - described as being of Caucasian appearance, about 180cm tall of slim build and with long blond hair - entering the service station and going directly into the bathrooms at the back of the store.

He then snuck out from the bathrooms wearing a white mask and gloves, and allegedly holding a gun. 

The man crouched behind rows of goods and made his way to the front of the store without the staff member noticing.

Owner Matthew Hill said that was "probably the scariest part", as he watched the CCTV footage on Monday morning.

"He calls [the staff member] and tells him to come here and give him his wallet," Mr Hill said, as the man appeared at the front of the store.

"He tells him to open the safe, but he's unable to do that."

"He ordered him back to the [cash register], told him not to be a hero, don't touch the emergency button and then just hand over the cash," Mr Hill said.

The staff member complied with the demands and the man fled with a small amount of cash from the register.

Mr Hill said he knew there was something wrong when his phone rang at 4.30am.

"I know I'm not answering the phone at 4.30am in the morning for anything that's good," Mr Hill said.

"He said we've just had a hold up and the guy had a gun."

Officers attached to Monaro Local Area Command were called and established a crime scene.

A replica firearm was located at the scene, which has been seized for forensic examination.

The man was last seen wearing a black hoodie, green vest, black pants, white runners and a blue baseball cap.

Police would like to speak to anyone who noticed any suspicious activity in the vicinity of Yass Road and Endurance Avenue about 4.15am this morning.

Investigations are ongoing.

Anyone with information is being urged to call Crime Stoppers on 1800 333 000.