The gang, who were wielding weapons, broke into the shop just before 11.20pm on Wednesday.
Police are appealing for any witnesses or information about the incident. They said the suspects were described as wearing dark clothing with hoods, face coverings and gloves.
No arrests have been made and the investigation is ongoing.
Detective Constable Sarah Hay, of Greater Manchester Police's Oldham district, said: "This was a carefully planned and brazen attack in which the offenders showed complete disregard for the property before making off with a quantity of cash.
"We are appealing for anyone who may have any information about this burglary, or anyone who was in the area at the time and witnessed anything suspicious to please contact police as soon as possible."
Anyone with information can contact police on 0161 856 9080 quoting incident number 3167 of 4/11/2020 or Crimestoppers on 0800 555 111.
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