A man has been arrested on suspicion of robbery after bystanders helped police identify the suspect.
The 30-year-old was detained following the incident at a shop in Saintfield Road area of the city on Wednesday evening.
Around 9.30pm, police received a report that a man armed with a knife - described as bald and wearing a hooded top with a scarf covering his face - had entered the shop and made off with a sum of cash.
When police arrived soon afterwards, members of the public identified the suspect a short distance away and he was subsequently arrested.
A knife was later recovered from a nearby drain.
Police have asked anyone who witnessed this incident to contact the CID at Castlereagh on 0845 600 8000. Or, if someone would prefer to provide information without giving their details, to contact the independent charity Crimestoppers and speak to them anonymously on 0800 555 111