Firefighters are urging the public to be vigilant following the latest in a series of blazes at the old Kirklees College building in Huddersfield.
The fire broke out just before 8.50pm on Thursday, and quickly spread.
Two rooms on the ground floor of the three-storey building in Portland Street were gutted, and firefighters had to battle to stop the fire spreading through the rest of the building.
Nine fire engines went to the scene, with crews from Huddersfield, Rastrick, Slaithwaite, Halifax and Dewsbury.
Six teams using breathing apparatus went into the smoke-filled building.
It took them over an hour to bring the blaze under control.
The former college has been the target for a spate of recent arson attacks.
Watch Commander Chris Bell, of Huddersfield fire station, said: “The two rooms were totally gutted and the fire was starting to spread, and the crews did a fantastic job in stopping it.
“The building is full of old furniture, and cables, and it could have been a dangerous situation had it spread.”
The cause is under investigation but it is being treated as a possible arson.
Watch Commander Bell said: “There have been a number of incidents there recently, and we would ask people to remain vigilant and let the police know if they see anything suspicious.”
Most of the college is due to be demolished to make way for a new development called Trinity Central which may feature a health care facility, veterinary practice and possibly a Lidl supermarket.
A large part of the site is occupied by what was the former Huddersfield Infirmary.
