The incident occurred on the Upper Newtownards Road area of east Belfast at approximately 1.00pm.
Detective Sergeant Arnott said the robbery had left members of staff in a state of shock.
“It was reported, just after 1.00pm, that a man had entered the shop, wearing a surgical mask and armed with a hammer.
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"He demanded the contents of the till and subsequently made off, with a sum of money, on foot in the direction of the Ulster Hospital."
DS Arnott added: “While no one was physically harmed, this has understandably been a distressing experience for the members of staff.
“I am appealing to anyone with information or who noticed any suspicious activity to contact us on 101, quoting reference number 944 of 02/06/20. We’re especially keen to hear from anyone who may have captured dash cam footage of the man leaving the shop or forecourt.”