Two armed men threatened two off licence staff and a customer then fled with an undisclosed amount of cash.
The pair entered Bargain Booze on Chorley Road in Adlington, Lancashire, wearing balaclavas and armed with a crowbar.
The raid happened at about 2020 BST on Tuesday, police said.
No-one was injured although one of the workers, who is heavily pregnant, was checked over and given the all-clear by a paramedic.
Det Sgt David Brooks, from Lancashire Police, said: "This was a terrifying experience for the people in the shop and although, thankfully, they were physically unharmed, they have been left incredibly shaken after what has happened."
Police are urging anyone who saw anything suspicious to contact them.