A robber armed with a gun threatened staff at two Wigan shops on the same day.
Police believe the same gun-wielding man targeted staff at Bargain Booze in Orrell and Wilkinson Newsagents in Newtown.
Staff were left "shaken" and anyone with information is being urged to come forward.
CCTV images have been released.
Two men went into Bargain Booze on Orrell Road, Orrell, at around 4pm on Tuesday.
The first man stayed by the door as the second approached the counter and demanded cash while brandishing a gun.
The staff member who was behind the counter locked himself in the storeroom.
The offender pulled at the door handle in an attempt to get inside, before he and his accomplice left with a case of beer.
Later that day, at around 5.15pm, a man who police believe to be the same man carrying the gun in the first robbery, entered Wilkinson Newsagents on Ormskirk Road, Newtown.
He approached the counter and demanded money from a female member of staff.
After the woman refused, the man pointed a gun at her and made the same demand, but she refused again.
The man stole a bottle of vodka and fled the store, heading towards Wigan town centre with another man who was standing by the door during the robbery.
The man who police believe is responsible for both robberies is described as white, 6ft tall, of athletic build and spoke with a Polish accent.
He was wearing a grey deerstalker-style hat with a peak at the front and ear flaps and a light-coloured jacket.
The other man is white, 5ft 8ins to 5ft 10ins tall, with short, brown hair and a distinctive red mark by his left eye. He spoke with a Polish accent and was wearing a dark blue top with grey sleeves.
Police have released CCTV footage showing both men inside Wilkinson Newsagents during the second incident, and CCTV images showing both men inside the two shops.
Det Con Brian Johnston, of GMP’s Wigan division, said: “These two robberies happened within 90 minutes of each other, at businesses within two miles of each other.
“We believe the same men were involved in both and I am appealing for the public’s help to assist us in finding them.
“Staff have been left shaken by the cowardly actions of these men and I would urge anyone who recognises the offenders in the footage or the photos to please get in touch.”
Anyone with information is asked to contact police on 101 and quote reference numbers 1388 or 1605 of December 6.
Alternatively, contact Crimestoppers, anonymously, on 0800 555 111.