Suffolk Police said shop assistants and customers at two stores in Ipswich have been left traumatised after they were threatened by an armed man.
The man, carrying what appeared to be a sawn-off shotgun, entered the Thresher wine shop in Bramford Road just after 2000 BST on Friday.
A second robbery took place shortly afterward in a shop on the Pinewood Estate.
Detective Harold Hayward said: "As you can imagine, a person entering any premises with a firearm, in this case we strongly believe it to be a sawn-off shotgun, is actually going to cause a great deal of distress.
"Both staff members and members of the public who were threatened by this person were obviously very distressed and traumatised."
Police have linked both raids and have appealed for witnesses.