The fire at Faughan Valley High School last night is thought to have been started accidentally, according to the Northern Ireland Fire and Rescue Service.
Fire fighters were at the scene until 12.44am this morning, Thursday.
The blaze started in external ducting on the first floor of the derelict school building, and the alarm was raised shortly after 8.30pm at Faughan Valley High School, at Drumahoe Road, and within minutes two appliances from Crescent Link Fire Station were joined by an appliance from Northland and an aerial ladder platform, as well as one appliance from Limavady, one from Dungiven, and an appliance from Kilrea Fire Stations as well as a Command Support Unit.
A spokeswoman for the NIFRS said: “Firefighters attended a fire on the first floor of a derelict school building. The fire was detected in external ducting on the roof. The incident was dealt with at 12.44am and the fire is thought to have started accidentally.