The Ontario fire marshal has been called in after Hamilton firefighters were called to a multiple-alarm fire in the central part of the lower city early Monday.
No one was found inside the building during a search and rescue operation.
The building appeared to be undergoing renovations and firefighters had to dodge a number of hazards inside, including holes in the floor.
One firefighter suffered a hand injury and was taken to hospital for treatment.
Damage is said to be extensive.
The cause of the blaze and the damage estimate have not been announced.