Fifty firefighters have been tackling a “significant fire” at the Bombardier factory in the docks area of Belfast.
The Northern Ireland Fire and Rescue Service (NIFRS) received a call at about 20:45 BST to attend the blaze on Airport Road in the east of the city.
The extent of the damage to the factory unit is not yet known, but there are no injuries.
Members of the public are being asked to avoid the area to allow operations to continue unhindered.
The aerospace company, Bombardier, is one of Northern Ireland’s largest employers.
In a statement, it said there were no employees working in the factory at the time, adding that it would take time to assess any damage.
The fire service said six pumping appliances, one aerial appliance, and a high-volume pump were being used to contain the fire.
Fire Service Area Commander Dermott Rooney said it was a “very significant” blaze and he and his colleagues would be at the scene for some time.
“Obviously, we are trying to get the fire under control. It’s very early stages, we would ask members of the public to stay away from the area so they don’t hamper our efforts,” he said.
“We’ve no indication of any particular risk to the local people, but they would be well advised to keep their windows and doors closed,” he added.
It is not yet known how the fire started.
The road has been closed to traffic.
DUP MP for East Belfast Gavin Robinson said it was “worrying news of a large scale fire in the factory”.
Alliance MLA for East Belfast Chris Lyttle said Victoria Park was also closed and that he was “grateful for the prompt response” of the fire service.