A wicked summer storm that swept through parts of southern Ontario Sunday evening left thousands in the dark as the severe weather system brought with it heavy rain, hail and high winds.

At one point during the storm, Hydro One said nearly 40,000 customers across parts of the province were left without power.

The utility company said "significant lightning" had resulted in power outages to its distribution system.

In Toronto, approximately 1,000 customers across the city were without power at the height of the storm. Many of those outages were reported in the area south of the Bathurst Street and Eglinton Avenue West, according to Toronto Hydro.

The powerful storm also blew out a transformer in the area of Lansdowne Avenue and Bloor Street West. According to a Toronto Hydro spokesperson, the blown-out transformer feeds approximately 2,200 customers.

Earlier on Sunday, Environment Canada issued a severe thunderstorm warning for Toronto. The national weather agency also warned that severe thunderstorms could produce tornadoes.

"Strong wind gusts can toss loose objects, damage weak buildings, break branches of trees and overturn large vehicles," Environment Canada said in a statement Sunday evening. "Go indoors and move away from windows and skylights."

Possible tornado north of Toronto

North of the city, Environment Canada is investigating a possible tornado that touched down in Proton Station, located west of Barrie.

Environment Canada meteorologist Tony Cham told The Canadian Press there were reports of roofs that were caved in due to falling trees in the Wingham area, located north of Stratford, Ont.

Ontario Provincial Police said officers also received reports of downed trees and power lines in the area, but it’s not believed the storm left behind any serious damage.

The national weather agency says it will likely send investigators to the area on Monday to survey the damage.