Three men armed with a hammer threatened supermarket staff in Northampton.
The three men made off with a small amount of cash after threatening staff at the Co-op Food Store in Bushlands Road on Wednesday night.
Police said all of the men were wearing hooded tops and were in their early-20s. No-one was injured in the robbery.
Officers are keen to speak to anyone who was in the Headlands area or at the store between 2030 and 2100 BST.
The first robber was described as white, about 5ft 11in (180cm) tall and slim.
He had blue eyes and wore a cream-coloured woolly sports hat with a logo on the front, a black scarf over his mouth and nose, and a light-coloured hooded top, grey tracksuit bottoms and cream racing-style gloves.
The second offender was also described as white, about 5ft 10in (178 cm) tall, slim and wore a dark-coloured hat and grey hooded top.
The third offender was described as black, about 5ft 11in (180cm) tall and larger than the other two men.
He wore a dark-coloured hooded top and had a scarf over his mouth and nose.