Police it happened on Gilnahirk Road before midday.
A woman entered the shop and engaged a female shop assistance in conversation before producing a knife and demanding money from the safe.
She made off on foot, in a countrybound direction, with a sum of cash.
The shop assistant has described the robber as in her 50s or 60s, 5′ 7″ tall, of medium build with missing upper front teeth.
She was wearing a black wide-rimmed ‘wedding’ style hat, black sunglasses, a black short sleeved blouse with a white floral pattern and black leather gloves.
Detective Sergeant Nigel Snoddy said: “The description is distinctive and we are hoping that witnesses will have noticed this woman in the area. Information can be given to detectives by calling the non-emergency number 101.
“Alternatively information can be given to the Crimestoppers charity anonymously on 0800 555 111.”