A member of staff at an Esso petrol station on the A45 near Earls Barton was threatened during a robbery in the early hours of the morning.
Three men stole cash and cigarettes after they entered the Esso service station on the eastbound carriageway between 12.10am and 12.20am.
During the robbery the men threatened a member of staff and forced him to lie on the floor. They put the stolen cash and cigarettes into a large Jewson bulk-bag, before escaping through the back door.
All three men were wearing dark clothing, balaclavas and gloves.
Officers are appealing for anyone who used the service station, or drove past on the A45, around the time of the robbery and who may have seen anything suspicious, to contact them.
Witnesses or anyone with any information can call Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111.