Twenty patients have been evacuated from a ward at Altnagelvin Hospital in Derry after a small electrical fire.
About 30 firefighters were called to the seventh floor of the hospital just before 10 o'clock last night.
No-one was injured in the blaze, which started in an electrical switch room.
It took firefighters about two hours to bring the fire under control, and the Western Health Trust has said that it is still assessing the extent of the damage.
Barry McDowell, district commander for the Northern Ireland Fire and Rescue Service told the BBC that six fire appliances were used in the operation.
He said patients had to be evacuated from the seventh and eighth floors, and a comprehensive search took place through the hospital from floor six to floor ten to ensure that there was no fire spreading throughout the hospital.
Although the fire was small, he said it produced "very pungent smoke", and spread quickly.
Mr McDowell said there had been good co-operation between firefighters and hospital staff to ensure everyone was safe, and there were no injuries.