He said the Fire Service was called to the school about 10pm a week ago after the same classroom was set alight. On that occasion, firefighters were able to get to the fire before too much damage was done.
He said the ramp and door to the classroom was burnt as well as some cabling.
"Unfortunately the building wasn't alarmed because last week's fire burnt the cabling and it hadn't been replaced yet."
Mr Anastasi said the classroom was near the fields and Elliott Cres, which was the back entrance to the school.
"One of the problems with the school is that it is open to everyone. It's difficult to keep an eye on the whole school."
The school's caretaker was on site at the time of the fire and was one of the many residents who called 111.
"With the school holidays at the moment, we tend to get an increase of incidents around schools. A lot of them are putting security fences around the perimeters now."
Senior Sergeant Malcolm Collins of the Rotorua police told The Daily Post the area was cordoned off last night and members of the Rotorua CIB and a fire safety officer were to conduct a scene examination early this morning.
Lakes High School's science block was the target of a suspicious fire in July 2010 which left extensive damage to five classrooms.