A shop worker suffered a "terrifying ordeal" after reportedly being threatened by a masked man wielding an 8in kitchen knife.
The suspect was described as being 5ft 11 (156cm), of thin build, who spoke with a southern Irish accent and wore a blue and white scarf over his face, police said.
The incident took place at a shop on Belfast's High Street at about 21:30 GMT on Saturday.
The man fled with a sum of money.
Officers said the staff member was not hurt, but was left badly shaken.
"This was someone who was simply doing their job at their place of work when what must have been a terrifying ordeal occurred," said Det Sgt Maguire.