A number of prisoners at the Midlands Prison in Portlaoise have had to be moved after a fire damaged parts of the jail.
The fire broke out in the attic area of E Division of the jail last night.
Officials at the Irish Prison Service said there is no power to most of the affected area and that all reasonable steps are being taken to rehouse prisoners that have to be moved.
The Irish Prison Service also confirmed that all the relevant safety systems worked as expected.
It is investigating the cause of the fire however, authorities say early indications would suggest the fire started as a result of an electrical wiring fault.
The fire brigade were called and the blaze was extinguished.
There were no injuries reported.
The Minister for Justice has expressed concern over the fire.
Charlie Flanagan, who is a TD for Laois, said thankfully no one was injured in the fire and he commended the fire service for their work.
Mr Flanagan said he has received assurances from the prison service that all relevant safety systems worked as expected.