Police were called to reports of a robbery at the McColl’s store in Barnes Lane, Dronfield Woodhouse at about 6.50am.
A spokesman for Derbyshire Police said: “A man with his face covered with a scarf walked into the store and demanded cash from a member of staff.
“The offender then fled with a small amount of money. He was white, of tall build, and was wearing dark clothing.
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“Our investigations are in their early stages but we are appealing for information from anyone who saw suspicious activity around the time.
“We also want to hear from anyone who lives nearby and has CCTV cameras that may have captured the offender.”
Concerned residents said an ambulance was spotted outside the store, following the incident.
Anyone with information is asked to call Derbyshire Police on 101, quoting reference number 131 of May 31.