Armed men smashed through the doors of a petrol station in Irlam and threatened staff with a gun.
Two thieves, who were wearing white face masks, approached the Texaco filling station on Liverpool Road at around 3.20am on Saturday 19 September.
The shop section of the station was closed, but the two men hurled a metal grid cover through the doors to gain entry, showering the floor with glass.
Once inside one of the men brandished a handgun to threaten terrified staff.
Greater Manchester Police confirmed that no shots were fired, but the two robbers got away with £500 in cash before speeding off in a silver car.
Officers are now studying CCTV in an attempt to identify the armed thieves.
Anyone who was in the area at the time, or has any information, is asked to call Greater Manchester Police on 101 or Crimestoppers, anonymously, on 0800 555 111.