A series of severe thundershowers have knocked out power to more than 40,000 Ontario customers on Saturday.

About 10,000 Hydro Ottawa customers were without power Saturday night as a fierce storm ripped through the capital city. Roofs were torn off homes, trees smashed into cars, leaving people trapped inside and there were reports of people seeing funnel clouds.

As of 9:30 p.m., Hydro One's website reported that 40,916 customers were without power.

Another hardest-hit areas was in Clinton, about 200 kilometres west of Toronto, where 5,931 customers were still without power Saturday night.

Between Clinton, Beachville, Lambton, Listowel, about 19,000 customers were without power.

In Fenelon Falls, Minden, Newmarket and Peterborough, nearly 9,800 customers were also waiting for power to be restored.

Closer to Toronto, nearly 5,000 Guelph customers, another 2,700 in Orangeville, as well as 1,000 in Alliston were without power.

In cottage country, more than 1,400 people lost power in Orillia, as well as more than 600 in Huntsville and 280 in Bracebridge.

At 9:30 p.m., Environment Canada's website said a severe thunderstorm watch was in effect for Hamilton, London, and much of the surrounding area.