Six fire engines and roughly 30 firefighters have extinguished a blaze at the Mater hospital in north Belfast.
Station commander Phil Burch has said that the fire broke out in a laundry room.
It was in the second floor of Dempsey Building, immediately alongside the several-storey high main building on the Crumlin Road.
The hospital houses a ward for newborn babies among its facilities.
The call was received at 4.08pm, after fire crews were notified by an automatic alarm system.
The Belfast health trust said that the hospital did not need to be evacuated of patients, but commander Burch said some staff were asked to leave as a precaution.
He said fire crews wearing breathing apparatus entered, put the fire out, and then used a fan to ventilate the building without any smoke reaching any of the critical wards.
He said the fire was “definitely accidental”, and that one possible cause may have been an appliance in the laundry room.
About 90 minutes after the call, the incident was declared over.