The robbery at 7.25am this morning at a convenience store in The Drive in Usworth.
The offender threatened a member of staff with a knife.
The member of staff was left shaken but not injured in the incident. A small amount of cash was stolen.
The offender is described as a white male, aged in his 20s, wearing a black hoody type and dark bottoms.
Officers are carrying out enquiries and appealing for witnesses.
Anyone with information is asked to contact Northumbria Police on 101 quoting reference 153 120517 or Crimestoppers anonymously on 0800 555 111.