Police, firefighters and paramedics are attending the scene at 85 East Liberty St.
The injured person suffered minor injuries, police say.
Firefighters say the explosion occurred on the sixth floor of the building. The doors of an elevator were blown out, along with the windows surrounding it.
The fire investigation is ongoing.
The TTC says buses are diverting along the 63 Ossington route as a result of the ongoing fire investigation at East Liberty Street and Pirandello Street.