Thunderstorms kill at least 5, knock out power in parts of Ont., Que.

As the May long weekend kicked off, a massive thunderstorm in southern Ontario brought strong wind gusts that knocked down trees, took out power and left at least five people dead.

Shortly after storms hit, police services across the Greater Toronto Area reported multiple power outages, downed trees and traffic concerns. After the storms cleared up in the Golden Horseshoe, the torrent of rain, wind and thunder made its way east toward Ottawa and southern Quebec.

In Brampton, Ont., Peel Regional Police reported that a large tree had struck a woman who was walking in the storm at around 1:30 p.m. EDT. The woman was transported to a local hospital where she later died.

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Ontario Provincial Police also reported that shortly before 12:30 p.m. EDT, three people were taken to hospital after a tree fell on a camping trailer at Pinehurst Lake Conservation Area near Cambridge, Ont. One of the individuals died after suffering serious life-threatening injuries while the other two had minor injuries, police said.

Ifficials say a 44-year-old man was also killed in Greater Madawaska, west of Ottawa, after reportedly being struck by a falling tree.

On Saturday evening, an Ottawa police spokesperson told reporters at a media availability that one person in the west end of the city had died after suffering “major injuries.”

Later Saturday, Gatineau police said a 51-year-old woman drowned after her boat capsized in the Ottawa River.

The storm ripped trees out by the roots and even knocked down hydro towers as it blew across Ontario and Quebec. A wind gust of 120 km/h was recorded at the Ottawa Airport at 3:30 p.m. Ottawa police said a barn in the west end of the city was destroyed, and many people were trapped in vehicles due to live wires on roads throughout the nation’s capital.

Police agencies and hydro providers are also urging residents to stay at least 10 metres from downed power lines as they may be carrying live electricity.

Both Hydro Quebec and Hydro Ottawa reported outages affecting more than 170,000 customers. Hydro One, which provides power to residents in rural parts of Ontario, reported that over 260,000 customers were without power as of early Sunday morning.

In Durham Region, Ont., just east of Toronto, the Township of Uxbridge also declared a state of emergency as emergency crews work to clear trees and other hazards from roads.

“Residents should be prepared for a prolonged power outage. Please stay home for safety,” the township said in a statement.

Environment Canada had warned that strong wind gusts could blast through at a speed of up to 100 kilometres an hour and residents could expect large hail the between the size of a nickel and a toonie to fall in certain regions.

"Large hail can damage property and cause injury. Strong wind gusts can toss loose objects, damage weak buildings, break branches off trees and overturn large vehicles," the agency said.

In a series of public weather alerts issued Saturday, Environment Canada had warned that weather conditions are "favourable for the development of severe thunderstorms" in these areas, including the Greater Toronto Area, Ottawa and Montreal.

Environment Canada said southern Ontario and Quebec are forecasted for heavy rainfall with high humidity levels over the weekend. Because of these conditions, The agency said it cannot rule out the possibility of tornadoes in some areas.

Environment Canada recommends taking cover "immediately" if threatening weather approaches.

"Remember, severe thunderstorms can produce tornadoes. Lightning kills and injures Canadians every year. Remember, when thunder roars, go indoors," the agency said.

According to forecasts, the severe weather is travelling northeast through the southern regions of Ontario and Quebec from Michigan, where a tornado there killed two people and injured 40 others on Friday.

With files from CTV News Toronto and The Canadian Press