Numerous wildfires are burning in Oregon’s forested valleys and along the coast, destroying hundreds of homes and causing mass evacuations.
Farther north, flames devoured buildings and huge tracts of land in Washington state.
Officials in the US said the number of simultaneous fires and perhaps the damage caused was unprecedented.
Several deaths were reported, including a one-year-old boy in Washington state. Oregon governor Kate Brown said communities have been “substantially destroyed” and warned there could be numerous fatalities.
Because of its cool, wet climate, the Pacific Northwest rarely experiences such intense fire activity. But climate change driven by human-caused greenhouse gases is expected to keep warming the region, with most models predicting drier summers, according to the College of the Environment at the University of Washington.
Mrs Brown said Oregon could see the greatest loss of life and property from wildfires in state history. The small towns of Phoenix and Talent in southern Oregon were heavily damaged. Another fire levelled most of the small farming town of Malden in eastern Washington — burning down the fire station, post office, city hall and library.
In Washington state, a fire burned more than 750 square miles of forest, brush and shrubland, Washington governor Jay Inslee said after a tour of the fire area.
Mr Inslee said low humidity, high temperatures and winds combined to probably make the blaze one of “the most catastrophic fires we’ve had in the history of the state”.
Fires were also causing chaos in California, where thousands of homes where threatened after winds whipped a blaze into a monster that incinerated houses in a small mountain community and killed at least three people.
Several other people have been critically burned and hundreds, if not thousands, of homes and other buildings are believed to have been damaged or destroyed by the fire north-east of San Francisco, authorities said.
Experts say California’s fires are growing bigger and moving faster than they ever have before.
In Oregon, fires erupted along Interstate 5, hitting towns and forcing a shutdown of the main road along the West Coast. US Highway 101, the main coastal highway running through California, Oregon and Washington, was also impacted.
At least three people in Oregon and the small child in Washington state were reported to have been killed. In Oregon, authorities said one of the victims from Marion County near Salem was a young boy.
The extent of damage was unclear because so many of the fire zones were too dangerous to survey, said a fire service spokesman in Oregon.
Catherine Shields evacuated her home in Silverton with a menagerie of animals, assisted by neighbours and strangers. As smoke obscured the sun and ash fell from the sky, they helped load her and her partner’s three horses, a donkey, two llamas, a dozen sheep, geese, ducks, turkeys and dogs onto trailers and vehicles.
As she walked one of the horses, she marvelled at how people were pulling together despite political divisiveness in the country.
“In the last 24 hours, we just felt people are doing their best,” Ms Shields said.
With an expected break in the weather, the chief of fire protection at the Oregon Department of Forestry said firefighters are hoping to turn things around.
“Today marks the last day where we are witnessing this historic weather event,” Doug Grafe said.
Officials said winds have slowed and cooler marine winds were expected.