No one was hurt as a result of either the smell or the evacuation, officials said.
The evacuation order came after workers detected a strange smell in the building, Capt. Mike Strapko of Toronto Fire Services told CBC News.
"Crews were told by some of the workers that people were smelling sort of an exhaust fumes and a gas type of smell," he said.
"We determined it was carbon monoxide and started to do a search through the building," Strapko said.
Firefighters eventually traced the smell to a burned out motor on the roof of the building, which had been pumping in carbon monoxide.