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Toronto's skyline was illuminated by intense flashes of lightning on Wednesday evening as heavy rain and winds hit the city during a powerful thunderstorm.

Environment Canada urged residents to take all necessary safety precautions during the intense weather. Local attractions including the Canadian National Exhibition closed down about two hours early as patrons sought shelter away from the fairgrounds.

A line of thunderstorms originating in Michigan had caused tornado warnings to be issued for part of the night over much of the southwestern Ontario region.

Residents from Windsor to Ottawa were also put on a tornado watch throughout the evening.

Environment Canada warned residents of the strength and damage-producing capabilities of the storms.

"These storms may produce large hail, damaging winds or heavy rainfall," the national weather agency said in a statement.

"Remember that some severe thunderstorms can also produce tornadoes."

Earlier Wednesday, Environment Canada issued watches for a sweeping area along Lake Huron and Georgian Bay.

A watch means conditions capable of producing severe weather exist. A warning means severe weather is either imminent or happening.

Geoff Coulson, an Environment Canada emergency preparedness meteorologist, told CTV News that the agency had "seen the ingredients coming together for a few days."

People should think about where they might find solid shelter for this evening if they are not at home, he said, adding, "Now would not be the time to take the family boat out on to Lake Ontario."

Goderich, Ont. lies on the shore of Lake Huron. A powerful, relatively uncommon F3 tornado struck the community on Sunday, devastating the town's centre and leaving one person dead.