Fire devastates historic Brisbane school

A suspicious fire has destroyed three buildings at a heritage-listed Brisbane school, and left a fourth badly damaged.

Students were turned away from Morningside State School on Tuesday as investigators picked over the remains of the gutted buildings and it will be closed for the rest of the week as they continue.

The students and their teachers will be relocated to Balmoral State High School for the rest of the week.

Officers say the size of the blaze suggests arson.

Queensland Fire and Emergency Services Chief Superintendent Lance Duncan said a significant portion of the school was lost.

"We've got three buildings that were interconnected and they were reasonably large structures," he told reporters.

"There's a lot of smoke still issuing from those particular structures at the moment, so it wouldn't be safe to have the kids here."

Two three-story buildings at the school were engulfed in flames by the time firefighters arrived about 3.30am on Tuesday. The flames quickly spread to other buildings.

Exclusion zones were enforced as the fire raged.

It took more than 50 firefighters to extinguish the blaze, which destroyed six classrooms.

Air quality tests have since allayed any concerns about asbestos in the air.

Queensland Department of Education said police and fire emergency services would likely be at the Morningside school for the rest of the week investigating and making it safe for students to return.

The school was opened in 1926.