Restaurant staff in Milton Keynes were threatened by a man holding a hammer and a hand gun.
During the robbery on Monday (March 6) a man entered the KFC restaurant in Barnsdale Drive, Westcroft Local Centre, and threatened staff, demanding they open the safe.
At around 9.21pm, unable to access the safe, the offender then ripped one of the tills from the counter and exited the restaurant through the drive through serving window, taking the till with him.
The offender fled the scene on a motorcycle.
No one was injured during the incident.
The offender is described as a white man, between 5ft 6ins and 5ft 7ins, with a slim build. He was wearing a black balaclava, a dark-coloured top, a black thick biker style jacket, black trousers and black boots.
Investigating officer, Det Sgt Phil Turner-Robson said: “This was a concerning incident in the community and we have now launched a thorough investigation in order to locate this offender.
“As part of the investigation, we would urge anyone who witnessed the incident or who may have seen or heard any suspicious behaviour in the area to please come forward.
“We would appeal to anyone with any information to please call the 24-hour Thames Valley Police enquiry centre on 101, quoting incident number 43170066547.”