Principal Ally Gibbons would not comment on the social media posts made by students or the cause of the fire while the police were still investigating.

Teenagers have taken to social media to congratulate a girl who claimed she was going to burn down Rotorua Girls' High School hours before a fire took hold of two classrooms.

"Tonight is the night to burn down girls' high", a post on Facebook by a Rotorua teen said.

Police are treating the fire as suspicious.

Mark Taylor/Fairfax NZ Principal Ally Gibbons at Rotorua Girls' High School.

The fire broke out in the stand-alone mathematics block at the school on Old Taupo Rd at 1.20am Wednesday.

Seven fire crews were called in to battle the blaze and managed to contain it to two classrooms in the block.

The Facebook post included the girl saying "only two classroom caught" when asked if she'd burned the school down.

Numerous posts and comments on Facebook followed, many congratulating the girl.

"Thank you, I got no school today whoop, could of done c block though, but shot, you've got some manly balls oie," said one.

Police would not go into detail when asked about the post, but said they were examining several social media posts as part of their investigation.

Another post claims that the girl was encouraged to burn down the classrooms and asked people to stop hating on her.

"what's been done has been done, there's no turning bacj (sic)".

Principal Ally Gibbons would not comment on the social media posts made by students or the cause of the fire while the police were still investigating.

"The fire is in the police hands."

She got a call at 1.30am alerting her to the fire.

"I came in straight away but their was no access in as the school as the road was blocked off so I had to wait to see what had happened."

The burnt classrooms were in their math faculty and were badly damaged. A lot of students' work and teacher resources had been lost.

"The two classrooms are badly damaged and we are very sad about that. Not only because of the structural damage but also because of all of the teacher resources and student work that were in those classrooms.

"It has been a very very sad day for my staff, students and the whole school community.

"Teachers have all knuckled down as this is our core business. The students are all in class and all learning. It is great we were able to operate as usual under the circumstances. "

Rotorua Detective Sergeant Richard Lang said the social media comments were being assessed as part of the investigation.

"However, it is not the only line of enquiry, and it is extremely important that people are not influenced by the comments to the point where they don't report information they have which might be relevant.

"We want to hear from anyone who may have information, no matter how insignificant it may seem.

An examination was continuing, but as a result of the initial assessment Police were treating the fire as suspicious, he said.

Concerned Rotorua Girls High School Parent Tere Piua said she was shocked and disappointed when she heard about the fire from her daughter, who saw it on facebook this morning.

"It is disgusting and sad that this happened in our community and for all of the other students that attended Rotorua Girls High School too.

"I was a little bit anxious this morning, asking my daughter if they knew who had done it. She told me they knew as it was all over Facebook.

"If the person that has done it was encouraged to by other students, it is very sad that this has happened and that that behaviour has instigated someone to damage a school."