Four workers were sent to hospital suffering from smoke inhalation after trying to extinguish the blaze which Toronto Fire says broke out in one of the machines at the Norampac paper processing plant on Evans Avenue in Etobicoke.
The 3-alarm fire broke out shortly before 10:40a.m. on Friday.
Toronto Fire says the damage is estimated at $500,000. The cause still isn't clear, but the Ontario Fire Marshall and the Ministry of Labour have been called in to investigate.
13 fire trucks and 65 firefighters were called out to battle the blaze.