Robbers are believed to have struck at the Co-op in Church Road, Hove, at about 5.30am today.
Sussex Police issued a statement saying: “Officers are currently on scene investigating the circumstances surrounding the incident.”
The robbery was reported just after 7am.
Last night two armed men escaped with an unknown sum of cash after holding up the Co-op just round the corner in Church Road, Hove.
Yesterday morning an armed robber made off with cash from the post office in Melville Road, Hove, near the Seven Dials.
The robberies have not been linked.
Anyone with information is asked to contact Sussex Police on 0845 6070999 or call the independent charity Crimestoppers on 0800 555111.