Classrooms damaged by fire at a Christchurch school may be demolished today.

Crews were called to the blaze at Russley School just after 7am.

A block of four classrooms has been gutted.

About 120 Year 7 and 8 students use these.

Principal Greg Lewis says he's supporting those affected and assessing when they may be able to reopen.

Senior fire officer Mark Elstone says representatives from the Ministry of Education are on site discussing demolition.

He says it will be traumatising for kids to spend the last two weeks of term looking at a burnt out skeleton of a classroom, so he understands why the Ministry wanted it gone.

Teachers say they are devastated and gutted.