Paramedics say a man was seriously injured following the blast in Mississauga, Ont., and a woman and child are being treated for minor injuries.
Mississauga Fire Chief Tim Beckett told reporters the blast caused a major fire, and he expects it will take a while to get it under control.
He says the building has partially collapsed, so firefighters have to battle the blaze from outside.
Photos and video from the scene show firefighters working to extinguish a flaming pile of rubble.
Beckett says a number of people who live nearby have been asked to leave their homes.