Just before 1.30am, a man armed with a knife entered the service station on Richmond Road and threatened staff.
The man fled on foot with an amount of cash, and was last seen running across the road.
No one was physically injured.
The suspect is described as being of Caucasian appearance, 170cm tall, slim build and dark hair. He was wearing a light coloured hooded top and grey tracksuit pants with white writing down the right leg.