A woman with a towel wrapped around her hand walked into a Valley Road establishment in the middle of the night and ordered a teenage cashier to hand over money in the till.
The incident was reported at 12.30am on Sunday, the police said.
Eyewitnesses told officers that a woman had walked into the Birkirkara shop and started pointing at employees with her hand, which was wrapped in a towel. She then ordered an 18-year-old cashier to give her cash in the till, took the money and fled.
A number of other employees were also present at the time. Nobody was hurt in the incident, the police said.
A police investigation is under way.