Toronto Fire Services Capt. Mike Strapko told CBC News the fire blew a door off a garage at St. Clair Avenue West and Bathurst Street.
He said he can't confirm the cause of this particular incident, but said similar cases are usually due to water getting into the vault.
Subway service has been suspended between St. Clair West and Union stations, according to a tweet from the TTC. It also said there is a power outage at Spadina station.
Shuttles are operating and no other subway lines are affected.