A masked man threatened a female cashier at Costcutter on Dryden Close, Maldon, with a gun during an attempted robbery last night.
The incident happened at 9.45pm when a masked man carrying a small gun entered the shop.
The cashier screamed and pressed the panic button, causing the man to run out of the shop empty handed.
The man is described as over 5ft 8inches tall and of medium build.
He was wearing a grey and white top, a black coat with a logo and trousers with reflective stripes at the bottom.
Anyone with information call Chelmsford CID on 101.