Cells had to be evacuated after a fire broke out at Channings Wood prison in South Devon.
Fire crews from Newton Abbot, Torquay and Paignton were alerted to the blaze at about 8pm on Friday and remained at the scene until the early hours of today.
It is understood prisoners had to be moved as smoke from a fire in the roof space took hold.
No-one was hurt and it is believed the fire started accidentally. Firefighters reported considerable smoke damage to the roof space of one of the wings.
A Prison service spokesman said: "The fire service were called to an incident at Channings Wood Prison. The fire is now out.
"This has affected one living block. There have been no reports of injuries to prisoners or staff."
