A man holding a knife and claw hammer demanded money from customers during a supermarket robbery in Newport Pagnell.
A staff member at Tesco Express in Elthorne Way fled the store and locked the doors on the offender at around 10.45pm on Tuesday.
The man then forced open the till and stole a quantity of cash before smashing the glass doors to the store and fleeing on foot towards Kingfisher Surgery.
He is white, about 5ft 8ins and of medium build. He was wearing a dark coloured hooded jacket and a scarf which covered his face. He spoke with a local accent.
Investigating officer, Det Con Greg Hughesof Force CID based at Milton Keynes police station said: “I would appeal to anyone who has any information about the incident to contact police via 101.
“If you saw anything suspicious or recognise the description of the offender then please come forward because your information could help our investigation.”