The incident took place at Betfred’s branch in Ellison Street, Jarrow, on Tuesday, July 9, at around 8pm.
A spokesman for Northumbria Police said: “The man was described as wearing a khaki colour top and dark trousers and was carrying what is believed to be a homemade weapon. He threatened the shopkeeper and demanded she empty the contents of the till.
“The offender is believed to have taken a quantity of cash before making off from the scene.”
The member of staff was unharmed and Northumbria Police confirmed on Wednesday morning that they were still searching for the robber.
A Betfred spokesman said: “The safety of our staff and customers is paramount and we are working with the police.”
Anyone with information is asked to call 101, quoting reference 945 090719.