Students are returning to an east-end Toronto high school on Monday after it was shut down nearly two weeks ago following a suspected arson.

Toronto District School Board officials said Danforth Collegiate and Technical Institute had passed air-quality tests and a large section of classrooms and study spaces have been deemed safe for re-entry.

Approximately 45 classroom spaces, technical classrooms and learning areas in the Donlands and Danforth Avenue reopened to students and teachers Monday morning.

A section of affected classrooms will remain closed for at least three weeks after being decimated by a fire sparked in a storage closet on April 25.

The partial closure means some students will split their time between Danforth Tech and nearby Eastern Commerce Collegiate Institute, with school buses shuttling between the two locations.

Danforth Tech had remained closed since the fire was discovered on the school's first floor by students in a drama class.

All 1,200 students and 160 faculty members evacuated the school safely, and a firefighter was treated at the scene for heat exhaustion.

Toronto police believe the three-alarm fire was set intentionally and continue to investigate the fire as arson.