About 150,000 customers were left without electricity Wednesday night after violent thunderstorms and high winds swept across parts of Ontario, and some may not have power restored for up to five days.

The severe storm ushered in cooler conditions following three days of extreme heat and humidity that had settled across much of southern and central Ontario.

Environment Canada said a trained weather spotter reported that a tornado touched down in the area of Highway 401 and Highway 6 at around 3:20 p.m.

At its peak, the storm's winds hit 120 km/h.

The storm caused flooding and downed trees and power lines across the province.

The province's electricity distributor said areas from Toronto north to Bracebridge and east to Tweed were affected by power outages resulting from trees falling on power lines.

Kawartha region hit hard

The area affected most was around Minden in the Kawartha Lakes region, where 23,000 customers lost power.

About 15,000 customers are without power in the Penetanguishene area in Simcoe County and 14,000 in the Tweed area in eastern Ontario.

Other affected areas include Barrie, Orillia, Huntsville, Newmarket, Peterborough, Kingston, Walkerton, Simcoe, Guelph and Orangeville.

Hydro One brought in extra crews to repair the damage overnight, restoring service for 20,000 customers, but warned that service might be out in the hardest hit areas for the next three to five days.

More adventure than expected

At a family camp north of Gravenhurst, campers and staff spent the night in the dining hall after the storm downed power lines inside and around the camp area.

About 30 campers and 100 staff were visiting Camp Pinecrest when the storm blew through around 7 p.m.

Organizers encouraged families to head home, but until early Thursday morning fallen power lines blocked roads exiting the camp.

Muriel Draaisma, who was at the camp with her two children, said the trip turned into more of an adventure than expected, but said spirits are still high.

No one was hurt.

Hydro One is urging people to be careful around downed power lines, even if a line appears to be dead, and asks them to report the fallen wires to the utility.