You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
Detective Tim Cook said the incident at the Collingwood Foodcentre on North Rd happened about 3am today.
"A man entered the store and threatened two staff members with a knife before leaving with cash and tobacco.
"While the victims were not injured in the incident, they are understandably very shaken and are receiving support."
The man is about 182cm tall, and was wearing a grey hoodie, blue jeans/chinos, a black balaclava and sunglasses, Det Cook said.
Police are appealing to the public for any information or sightings of the man.
Call 105, quoting file number 191109/3839.
Information could also be provided anonymously to Crimestoppers on 0800 555 111.