About 1.48pm yesterday afternoon, Fire Rescue Victoria responded to several reports of a fire at the Heatherwood School, 370 Springvale Road, Donvale.
The first on-scene firefighters escalated the response to a second alarm with the first FRV crews arriving on scene in 4 minutes to find a fire through the roof of one building.
Detectives are investigating a fire that has caused significant damage at a Donvale school.
Investigators understand an unknown male attended the Springvale Road school at about 1.30pm yesterday.
The northwest corner of the building was set on fire from inside and the male was last seen exiting the school and fleeing on foot towards Springvale Road.
The fire has destroyed five classrooms and a canteen. The roof has collapsed.
The suspect male is described as being Caucasian, 180cm tall with a thin build, dark hair and aged in his 30s.
He was wearing a black hooded top, a black and white paisley bandana covering his face and may have been carrying a black Nike backpack.
A crime scene has been established while detectives work to establish the exact circumstances and cause of the fire.
Eleven trucks and 44 firefighters brought the fire under control, containing it to one 50 x 20m wing of the building.
The fire was deemed under control an hour later.
Crime Stoppers 1800 333 000 or www.crimestoppersvic.com.au.