Around 4.30pm a man entered Ladbrokes on High Street, Lanark, with a scarf across his face and threatened staff.
He demanded money and made off in the direction of the Delves Park area.
No-one was injured in the incident; however, members of staff were left badly shaken by the incident.
CCTV footage is being checked by officers as they try to obtain further detail about the suspect who was wearing a red, white and blue scarf across his face when carrying out the robbery.
Police describe the the man as around six-feet tall, and of slim build.
He was wearing an Adidas hooded top at the time of the incident.
Detective Sergeant Scott Wilson, from Wishaw CID, said: “I’m appealing for anyone with any information to contact us regarding this robbery.
“Perhaps you saw the man acting suspiciously prior to the crime taking place or you noticed him running off toward Delves Park?
“We are conducting door to door enquiries and analysing available CCTV.
“Any information you have, no matter how small, could make a real difference as part of our broader investigation.”
Anyone with any information is asked to contact CID officers at Wishaw Police Office on 101. Alternatively, they can call Crimestoppers on 0800 555 111 where information can be given anonymously.
Police are not linking this to a robbery at Ladbrokes on Main Street, Blantyre the previous day.