Firefighters responded about 3:30 p.m. when smoke from beneath the street began to fill the air along Madison Street.
Firefighters said they believe an underground electrical transformer exploded.
Crews closed Madison between North Erie and North Huron streets. Authorities evacuated the Louisville Building and Martini and Nuzzi’s as a precaution, fire officials said.
The street remained closed into the evening as firefighters and Toledo Edison crews investigated the explosion.