Environment Canada says a tornado touched down in Ottawa and Gatineau, Que., on Friday afternoon as much of southern Ontario saw severe thunderstorms and high wind gusts.
Peter Kimbell, a meteorologist with Environment Canada, says the tornado overturned cars on Highway 50 in Gatineau and caused extensive damage to houses in Ottawa's western area of Dunrobin.
The Ottawa Hospital tweeted Friday night that it was treating six people with storm related injuries, including two who were in critical condition.
Trees and power lines were torn down over a wide area, knocking out the electricity to tens of thousands of hydro customers.
A more complete assessment of casualties and damage is expected later today.