A powerful storm clobbered Washington state on Wednesday, knocking out power to hundreds of thousands of people while disrupting road travel and causing at least two deaths and two injuries.

Winds should die down across the region by midday, but the storm has moved to California and is set to bring extreme rainfall by the end of the week, according to forecasters.

A woman was killed on Tuesday when a tree fell on a homeless encampment in Lynnwood, north of Seattle, local officials said. A second woman was killed near Seattle when a tree fell on her home, Bellevue officials said. Two people were injured when a tree fell on their trailer in Maple Valley, southeast of Seattle.

The storm with tropical-storm-force winds of 80 km per hour and gusts around 110 kph felled trees and power lines overnight. More than 530,000 homes and businesses in Washington, southwest Oregon and Northern California were without power, according to Poweroutage.us, down from more than 600,000 earlier.

The windstorm and heavy rain also damaged the power system in Canada's Pacific coast province of British Columbia and cut power to some 225,000 customers Tuesday night, according to provincial electricity provider BC Hydro. By Wednesday morning, about 100,000 customers, mostly on Vancouver Island, remained without power.

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An NBC affiliate in Seattle broadcast images of cars smashed by fallen trees and damaged homes.

The Snohomish Regional Fire & Rescue service in western Washington urged residents to stay home, with many trees and power lines down.

“Trees are coming down all over the city & falling onto homes," the fire department of Bellevue posted on social media. "If you can, go to the lowest floor and stay away from windows. Do not go outside if you can avoid it.”

Schools across western Washington canceled classes or postponed the start of school on Wednesday.

"The storm is just beginning," said Rich Otto, a meteorologist with the National Weather Service's Weather Prediction Center in College Park, Maryland.

"We haven't gotten a ton of rain yet, just two to 5.1-7.6 cm over southwest Oregon and northern California," Otto said.

'Bomb cyclone'

The storm, called a "bomb cyclone" when the storm rapidly intensifies, will stall over Northern California in the next few days, Otto said. On Friday, rainfall could reach up to 51 cm in parts of southwestern Oregon and northern California, Otto said.

A bomb cyclone rapidly intensifies in 24 hours or less when a cold air mass from the polar region collides with warm tropical air in a process that meteorologists call bombogenesis.

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The weather service has issued warnings and watches across the US Pacific Northwest for high winds and flooding, including blizzard warnings, from northern Washington to the Sierra Nevada Range.

The Washington state's transportation department warned motorists to be cautious while on roadways as downed trees and weather conditions slowed traffic across the state.