A masked man carrying a "cross bow type weapon" has raided a garage in Denbigh.
North Wales Police said the thief made off with cash after targeting Morrisons Garage on Smithfield Road at about 1955 GMT on Tuesday.
Officers are appealing for help in tracing the robber who they said was white, about 6ft (1.82m) tall, and between 25 and 30.
Police, who are examining CCTV footage, said staff were shaken by the ordeal but no-one was injured.
They are also trying to establish whether the weapon used in the raid was real or an imitation.
The man, who police said had an athletic build, was wearing black clothing and a black balaclava.
Det Sgt Craig Adshead said: "The offender made his getaway with an unknown amount of cash.
"No one was hurt during the incident, although the members of staff were shaken.
"We are examining CCTV footage and would ask anyone who was in the area at the time and may have seen anything unusual or suspicious or may have any information regarding the offence to contact St Asaph CID immediately."
Contact North Wales Police on 101 or Crimestoppers anonymously with information on 0800 555111.