Environment Canada has confirmed two powerful tornadoes ripped through west end Ottawa before touching down again in Gatineau across the Ottawa River.
Officials say dozens were hurt and at least two residents are in hospital with critical injuries.
Tens of thousands were left without power after at least 80 utility poles either snapped or were damaged.
Meteorologists say severe thunderstorms spawned one twister classified as an EF-3 with winds up to 265 km/h while another tornado was an EF-2 with winds up to 220 km/h.
Tornadoes are not uncommon in Southern Ontario but storms of this strength are rare.