A three-alarm fire that led to an evacuation of an East York high school on Wednesday has been deemed arson, Toronto police said Friday afternoon.

The blaze, which is believed to have started inside a storage closet in a second floor drama classroom, broke out at around 10:17 a.m. at Danforth Tech near Danforth and Donlands avenues.

"Something within the classroom was set on fire," Const. Tony Vella told CTV News. "We are currently looking at who is responsible for it."

As a result of the fire, students have been attending classes at alternate locations.

Grade 9 and 10 students are attending Eastern Commerce Collegiate Institute and Grade 11 and 12 students are attending Monarch Park Collegiate Institute.

According to Chris Broadbent, manager of health and safety for the Toronto District School Board, it could be sometime before classes are back in session at Danforth Tech.

"It's still to be determined," he told reporters Friday afternoon. "We have a late start on Monday and that will allow the staff to meet in the morning and look at the next steps, and we will move forward from there on making sure we have accommodations for students to continue their education for the rest of the year."

Broadbent said the blaze resulted in smoke damage throughout the school and some water damage in classrooms below the second floor drama room, where the fire is believed to have started.

He said a "significant" amount of glass was also broken to ventilate the school.

"As far as an estimate of damages goes we don't have that yet," he said. "We haven't even been officially given the school back."