A man armed with a firearm entered the post office in Rivett Place about 8.30am and demanded money from the cash register while threatening staff and customers, though no one was injured.

The man fled the store with a sum of cash. He was last seen running along the pedestrian pathway after crossing Bangalay Crescent, Rivett.

While fleeing, the man discharged the firearm into the air after several witnesses followed him for a short distance.

The man is described as Caucasian, between 165cm to 175cm tall with a slim build and brown eyes.

At the time the man was dressed in dark coloured clothing and sneakers with a dark coloured cloth covering his face. He was also carrying a dark green plastic shopping bag.

Police urge anyone who may have any information that could assist to contact Crime Stoppers on 1800 333 000, or via the Crime Stoppers ACT website. Please quote reference 6178618. Information can be provided anonymously.