The building is located at 2550 Pharmacy Ave., just south of Finch Avenue East.
Fire officials say the fire is in the main electrical room in the basement.
Smoke was visible when firefighters arrived.
A woman was stuck in an elevator, but she has since been freed.
Paramedics say a male patient suffered minor burns to his hands and has been taken to hospital.
A second patient may also have a minor burn, they say.
Toronto police say the building is being evacuated.