Five men robbed the Shamrock Supermarket in Kraaifontein of R300 000 cash on Sunday, police say.
Police arrested a 31-year-old man on the same day. They say they found him hiding with R5000 and a gun used in the robbery at a house near the Brighton Road supermarket.
Kraaifontein police spokesman Captain Hein Hendricks said they were searching for the remaining suspects.
Calls to the Shamrock supermarket went unanswered.