Two inmates of Buckley Hall prison, in Rochdale, Greater Manchester, are reportedly protesting on the roof of one of the buildings.
Police are at the scene including specialist negotiators trying to talk the men into coming down.
Prison visiting has been cancelled for the day.
In a statement, the Prison Service said: “There is an on-going incident at HMP Buckley Hall. Two prisoners gained access to the roof this morning. “Specialist staff are at the scene working to bring the situation to a safe conclusion.”
The situation was concluded at approximately 1pm.