Around 20 inmates were evacuated from a cell block at Kirkham Prison after a fire broke out.
Firefighters were called to the open prison (pictured) shortly after midnight on Saturday after reports of a fire in the roof space of an admissions centre. Light smoke damage was caused to the roof.
The cause is still unknown but officers suspect an electrical fault is to blame.
Around 20 inmates were temporarily rehoused while fire crews from South Shore and Wesham investigated the incident.