Streets around Queen's University in Belfast were sealed off last night after a chemical spillage in its medical and biology centre.
About 60 firefighters attended the centre in the south of the city after reports of fumes seeping from the building.
The centre was evacuated and officers wearing breathing apparatus searched the building.
Fire and Rescue Service area commander Chris Kerr said they were moving cautiously because of the large quantity of chemicals in the centre.
READ MORE
He predicted the operation would last way into the night before the all-clear could be given.