Fire crews were called to St Thomas More RC Academy on Lynn Road at 2.17am.
Tyne and Wear Fire and Rescue Service said a metalwork room and adjacent wood store in the design and technology block has been severely damaged in the blaze.
Six classrooms and two offices have also been severely smoke-damaged.
Twenty firefighters and five fire engines from Tynemouth, Wallsend, Gosforth; Hebburn and West Denton attended.
Crews, some using breathing apparatus, quickly extinguished the fire to ensure it didn’t spread and cause further damage.
The school is closed today as a result.
Headteacher David Watson, in a message on the school’s website, said: “Due to this morning’s fire, the fire alarm system and telephone line in most of the wider school has unfortunately been compromised. This was only discovered when a fire alarm engineer came on site.
“We therefore have no alternative but to close the school for all students today, Tuesday 10th July. As soon as we have anymore information we will let you know.
“Any students who are already in school have been informed and those that can, will make their own way home. I am sure you understand that we need to put the safety of students and staff first. If this is a problem for any of the students we will keep them in school until other arrangements can be made.
“I sincerely apologise for this very late notice but hope that you understand how fluid the current situation is.”