A 15-year-old boy has been arrested and charged over a fire which razed a Bay of Plenty high school block.

The teenager will be held in police custody until his appearance in the Tauranga District Court tomorrow, a police spokeswoman said.

Police and the Fire Service were called to the suspicious fire at Te Puke High School about 4am yesterday.

Principal Alan Liddle said a single-storey block of five classrooms used for wood and metal work was destroyed.

Dozens of students' course work was also ruined and the school would be contacting the New Zealand Qualifications Authority about what could be done to salvage the assessments.

Firefighters arrived at the scene shortly after 4am but by then the blaze had taken hold.

Among the twisted and charred remains of the gutted classrooms are a few vices in the woodwork room. Some staff also managed to salvage some materials.

"But all of these things are water-logged and hopeless, it's just an awful situation," said Mr Liddle.

"It will have a huge effect on the teachers and students and a huge effect on the whole community as well."

Mr Liddle could not estimate the size of the bill, although replacing the classrooms and all the woodwork, engineering, graphics and textiles materials was likely to cost hundreds of thousands of dollars.

"If you could think of possibly the worst thing that could happen, this is probably it," he said.

The technology department was used by most of the school's 1070 students.

Locals living nearby told the Herald they were awakened by the sound of fire alarms and windows breaking in the intense heat.

Lynne Clay, head of the school's board of trustees, said she could see the flames and smoke from her home.

"When I realised what it was I thought 'oh my God, that's our school'. It's not what I had planned for Easter," she said.

Te Puke volunteer fire brigade deputy chief fire officer Dale Lindsay said the fire was well ablaze by the time crews arrived.

Firefighters were still dampening hot spots at 10am yesterday. "What makes this hard is that there are a lot of firefighters whose children go to this school," he said.

Mr Liddle said the only saving grace was that school authorities had two weeks to prepare temporary classroom arrangements with the Ministry of Education as students were away on holiday.

But it was unlikely the children would have proper classrooms by the end of the year.