Two men with a blunt weapon targeted the Scotmid store in Greenock, Inverclyde.
Police said the staff, an 18-year-old man and a woman aged 26, had been left traumatised by the violent robbery on Monday morning.
The men demanded cash before assaulting the assistants in the Murdieston Street shop. The staff were not seriously hurt, and the pair made off in a small light-coloured vehicle.
Appealing for witn-esses, Detective Ins- pector Julie Henry said: "This was a horrendous attack."