The first robbery happened at the Co-Op, High Street, Finedon, at about 10.20pm on Wednesday, November 30.
This was followed just 20 minutes later by a robbery at the Co-op in High Street, Earls Barton.
In both incidents, three men entered the shop and threatened staff with weapons, before making off with cash and cigarettes.
Police are appealing for witnesses, particularly anyone who may have seen a vehicle travelling at speed between the above locations.
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They would also like to hear from anybody who has been offered cigarettes for sale.
Anyone with information can contact Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111.