A robber threatened newsagent staff with a claw hammer before making off with £90 in Cosham.
Detectives are appealing for information after the robbery, at the McColls shop in Chatsworth Avenue, on Friday night.
At around 8.30pm, a man entered the shop with a scarf tied around his face.
He threatened two female members of staff with a claw hammer.
The robber made off with £90, and ran off towards Hawthorn Crescent.
The man is described as white, thin, with pale skin and short brown hair.
He wore a large pink woolly hat and a scarf across his face.
He had a dog that looked similar to a Staffordshire Bull Terrier and wore a dark-coloured top, a baseball cap,. and a coat.
DC Andrew Larder said: ‘This was a terrifying experience for the staff and I would appeal to anyone in the area who has any information or can help with the identity of the male with the dog.’
Anyone with any information is asked to contact DC Larder at Fratton CID on 101 or the charity Crimestoppers line on 0800 555 111, where information can be left anonymously.