Fireworks are understood to have been found at the scene of a fire which destroyed part of a school block in Hamilton last night.
Police have yet to confirm the find but said there were reports of fireworks going off at the time the fire began at 11.45pm.
They said the blaze that engulfed part of a school block at Sacred Heart Girls' College is being treated as unexplained.
Fire and Emergency northern communications shift manager Jaron Phillips said firefighters were called to the blaze in Hamilton East just before midnight.
"Fire crews found the upper level ablaze and immediately called for back up."
Phillips said 14 crews and 60 firefighters were scrambled to the scene from across the Waikato including from Ngaruawahia, Te Awamutu, Cambridge and Morrinsville.
Waikato senior specialist fire investigator Peter Hallett, who was at the school this morning, said it appeared the fire began on the second level of the two-storey block.
Hallett said one classroom, a staff room and resource rooms at the Catholic school were damaged in the fire.
Downstairs classrooms were waterlogged after firefighters spent four hours bringing the fire under control.
Debris was strewn outside the rooms and windows had been shattered.
He said it was being treated as "potentially suspicious" until determined otherwise.
Hamilton Police detectives were also at the scene on Firth St and were in charge of the investigation.
Phillips said firefighters managed to stop the fire spreading to other classrooms by cutting it off.
Waikato Police CIB Acting Detective Sergeant Ian Foster said the fire caused extensive damage to the building, "which is not only a terrible blow for the students and teachers, but it will result in a substantial financial loss to the school".
He said police were seeking information relating to the fire and what was happening in the area earlier that night.
"There have been reports of fireworks going off near the school. Police want to hear from anyone who has information about the fire or anyone who was setting off fireworks near the school last night."
Witnesses can call Hamilton Police on (07) 858 6200 and quote file number 171111/0641.
Or to report information in confidence call CrimeStoppers on 0800 555 111.