At around 9.30pm on Friday, November 4, three masked men went into Tesco Express on Manchester Road, Westhoughton, carrying crowbars and a machete-style knife.
Two of the men ushered a member of staff into a store room, then into an office while holding the knife against the back of the staff member’s head.
They then ordered another member of staff to hand over a significant amount of cash.
The black Ford Focus Zetec in which the offenders arrived and left the supermarket was later found burnt out on Heatons Grove.
Police have now released CCTV footage of the robbery as they continue to investigate.
Detective Constable Pamela Chandler, of GMP’s Bolton Borough, said: “This was a terrifying experience for staff who were threatened at close quarters with a large knife and were left utterly shaken by the actions of these cowardly individuals.
“At least one customer also witnessed this traumatising incident.
“I would encourage people to carefully watch the CCTV footage. Even though the offenders are masked, you may still recognise something distinctive about them which could help with our investigation.
“I am also appealing to any witnesses or anyone who feels they have any other information in relation to this robbery to please get in touch.”
Anyone with information is asked to contact police on 101 and quote the reference number 2328 of 04/11/16, or the independent charity Crimestoppers, anonymously, on 0800 555 111.