United Airlines and other airport workers were forced to evacuate as a two-alarm fire broke out in a maintenance facility at San Francisco International Airport.
A large plume of smoke was seen rising from the hangar early Wednesday and was visible for miles around.
No injuries were reported.
The cause was likely a faulty air conditioning and heating system located on the roof, said Doug Yakel, an airport spokesman.
It took fire crews about one hour to extinguish the blaze.
The maintenance facility is located north of the main airport terminals and the fire did not impact any flight operations.
United Airlines officials are assessing the damage which seems to be restricted to the roof.
