This photo was taken on Sunday from a Toronto balcony, looking east from the Yonge and Steeles area. (Submitted by Karim Ismail)

People in southwestern Ontario are cleaning up debris and repairing damage Monday after severe storms, fuelled by intense heat and humidity, battered a swath of territory between Windsor and Toronto.

The weekend's high temperatures and humid conditions continued into Monday, with officials warning of the effects of heat on vulnerable members of the public.

There were reports of tornadoes or funnel clouds Sunday in at least three places. Environment Canada says it will investigate the sightings and examine the damage caused by thunderstorms.

The weather agency's Geoff Coulson says satellite images showed a "classic tornado shape" to clouds near London, Ont.

The combination of heat and cold lake water created a haze for boaters near Toronto on Sunday. (CBC)

Intense weather also hit New Brunswick and Saskatchewan Sunday, with Environment Canada issuing severe weather alerts and warning that tornadoes were possible.

The warnings were downgraded late Sunday night. There were reports of a funnel cloud near Weyburn, Sask.

Environment Canada's tornado warnings for Ontario also included the city of Toronto and adjoining areas. Those warnings were withdrawn Sunday evening.

Television pictures coming into CBC from the region show downed power lines, fallen trees and damaged roofs.

Residents of Dresden, Ont., spoke of high winds, flying debris and heavy rains.

Storms, heat and humidity to continue

Reports from Kitchener-Waterloo say hundreds of people were without power for a short time after lightning struck hydro poles.

Repair crews were able to restore electricity to the worst-hit areas within an hour or so, local media report.

As investigators look into damage and try to confirm funnel cloud sightings Monday, more storms are forecast.

The high heat and humidity that helped spawn Sunday's storms are still affecting southern Ontario, Quebec and the Maritime provinces, forecasters said.

Toronto's medical officer of health, Dr. David McKeown, placed the city under an extreme heat alert Monday as temperatures reached the low 30s, but felt like 40 because of the high humidex ratings.

Members of the public were told to check on housebound family members and acquaintances. Those who work outdoors were advised to use sunblock, drink water and avoid prolonged exposure or undue exertion.

The northeastern U.S. states are also experiencing unseasonably high temperatures, with Monday's high for New York City forecast to be around 38 C.

In the U.S. Midwest, the same severe weather system has brought storms, torrential rain and flooding that left eight people dead and stranded thousands in Iowa, Wisconsin and Indiana.

With files from the Canadian Press