A female attendant at a service station in East Corrimal was threatened with a knife shortly after 4pm on Thursday.
Wollongong District Police officers established a crime scene after a man entered a Caltex service station on the corner of Railway Street and Pioneer Road.
The victim told police the man was armed with a knife and threatened the attendant.
He obtained a small amount of cash before fleeing the service station.
The man was seen heading north along Pioneer Road on a child's Razor-style scooter before witnesses lost sight of him.
Acting Inspector Darren Kelly said the female attendant was not injured but was "visibly shaken".
At 5.30pm, police had taped off the station and were still gathering evidence.
The man is described as being in his mid to late 20s, 165cm to 170cm tall, olive complexion, short dark hair and he was wearing a black cap, black pants and black hoodie jumper.
Police are continuing their investigation and are calling for witnesses to come forward and contact Crime Stoppers on 1800 333 000.