A total of 64 prisoners had to be evacuated from a section of HMP Guys Marsh near Shaftesbury after a fire broke out on a roof at the prison on Friday night.
According to the BBC, an inmate scaled the roof wearing multiple sets of clothes before setting light to them and triggering the ‘large fire’ at around 8pm.
The inmate was drunk and protesting against changes to the prison regime, it was reported.
A spokesman for Dorset Police said all prisoners had been accounted for and there were no reports of any injuries.
One prisoner who was reported to be on the roof of the prison building during the incident had been brought back down to safety and been checked over by paramedics as a precaution, added the spokesman.
Officers from Dorset Police remained at the scene to assist Dorset & Wiltshire Fire & Rescue Service and Prison Service staff.
Superintendent Caroline Naughton, of Dorset Police, said: ‘This was an isolated incident. An investigation is now underway to establish the exact cause of the fire. These enquiries remain ongoing.
‘We would like to reassure members of the community that there is no immediate risk to those living in the surrounding area and that the incident is under control.’