A prisoner was taken to hospital after the air ambulance was scrambled to a jail in Rochdale.
Bosses say it was an "isolated incident" and that no other prisoners were harmed.
Emergency services attended HMP Buckley Hall after they were called around 9:50am this morning, Wednesday November 25.
Eyewitnesses saw the helicopter landing in the car park outside the prison with medics heading inside the prison walls.
A spokesman for the North West Ambulance confirmed they sent two ambulances, a rapid response vehicle and an air ambulance to the scene.
One male patient was conveyed to hospital in one of the ambulances he added.
No further details about their condition or the nature of their injuries were given.
A Prison Service spokesman said: “A prisoner has been taken to hospital after an isolated incident this morning.”
It is understood no other prisoners were injured.
Situated north of Rochdale town centre in the Buckley area of the town, HMP Buckley Hall is a category C male prison named after a historic house which once occupied the site.
It has a capacity of just under 450 with prisoners mainly housing inmates from Manchester sentenced to terms of four years or over.
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