Police are investigating robberies at eight separate properties and believe the crimes could be linked.
Five occurred at sports clubs, while others took place at social clubs and licenced premises. They were committed between October 2016 and January 2017.
The first crime happened at Rochdale Cricket, Lacrosse and Squash Club at around 1.55am on Sunday 2 October 2016.
Three unknown men armed with an axe and a hammer approached two staff members outside the club and forced them inside.
They threatened to harm staff if they did not hand over money and eventually fled with an amount of cash, leaving all the staff members locked in the office.
The most recent happened at around 11.30pm on 15 January when three men forced their way into Chadderton Cricket and Bowling Club on Bowling Green Lane.
The offenders, one of whom was carrying a crow bar, entered the bar area and demanded cash, while another stopped customers from leaving the club.
One of the men, armed with a metal-ended pool cue rest, grabbed a female member of staff by the neck and forced her to open the strong room.
On two occasions she was dragged to the ground and viciously beaten with the metal end of the cue rest.
The offenders stole a quantity of cash, while the member of staff was taken to hospital. She has since been discharged, but has been left traumatised, with severe bruising to her face and body.
Detective Roger Smethurst, of GMP’s Serious and Organised Crime Group, said: “What started as a handful of seemingly isolated robberies has become a noticeable trend, predominantly at sports and social clubs and often around closing time.
“Some of these crimes have been extremely violent, leaving staff with injuries and customers totally distressed by what they have been forced to witness.
“I am appealing to witnesses to any of the incidents, or anyone who believes they have any information, to please get in touch.
“I would also like to remind people involved in the running or management of sports clubs, social clubs and licenced premises in remote locations to be aware of their security at this time of heightened risk.”
