Oregon officials say they are preparing for a large number of deaths from this week’s wildfires, with at least five people killed and dozens more missing amid blazes that have burned more than 1 million acres statewide.

The wildfires have put an estimated 500,000 residents, or over 10 percent of the state’s population, under an evacuation warning or order. Gov. Kate Brown (D), who earlier this week described the wildfires as a “once-in-a-generation event,” said Friday that about 40,000 people have evacuated.

Authorities are preparing for “a mass fatality incident based on what we know and the number of structures that have been lost,” Andrew Phelps, director of the state’s Office of Emergency Management (OEM), said Friday. Oregon defines a mass fatality incident as one that causes death and suffering “that cannot be met through usual individual and community resources.”

Communities all along the West Coast have been battling wildfires affecting tens of millions of people — tearing through towns, forcing mass evacuations and fouling the air. Scientists call it a “compound disaster,” in which many extreme events unfold at once, and have been warning such widespread destruction is the inevitable result of human-caused climate change.

In Washington state, Gov. Jay Inslee (D) said Friday that nearly 627,000 acres had burned in the state since Monday — creating Washington’s “second-worst fire season” on record within just five days. “And these are just the active fires, not the ones that have already been contained and where recovery continues,” Inslee said at a news conference.

A Northern California wildfire, the North Complex Fire, has burned through more than 250,000 acres of land and killed at least nine people, part of a brutal fire season that includes six of the 20 largest wildfires in the state’s history. Butte County sheriff’s officials said Friday that 19 people remain missing in the state’s deadliest blaze this year.

“California, folks, is America fast forward,” California Gov. Gavin Newsom (D) said Friday at a news conference, the sky behind him hazy with smoke. “What we’re experiencing right here is coming to [communities] all across the United States of America unless we get our act together on climate change.”

In Oregon, the number of evacuees spiked Thursday when many residents left communities in Clackamas County, the state’s third-most populous county, which borders Portland, said Paula Fasano Negele, a spokeswoman for the OEM.

Those evacuations came after officials warned in a news conference that the Riverside Fire, which originated in Clackamas County, was expected to merge with another one of the state’s largest wildfires, the Beachie Creek Fire of Marion County. Those two wildfires have scorched more than 300,000 acres at about zero percent containment, decimated homes and businesses, and left thousands displaced, according to the Oregon Department of Forestry.

“I’m here, and I still can’t even fathom what’s happening,” Negele told The Washington Post early Friday.

The good news, Brown said Friday: The weather “fueling these fires over the past days has finally broken down,” she said, meaning authorities expect some relief from cooler air and moisture in the coming days.

Brown also said her request for federal aid — firefighting resources, search and rescue aid and temporary housing for those displaced — has been approved.

Improving weather meant firefighters should be able to move from a defensive stance to an offensive one in the next few days, Doug Grafe, chief of fire protection at the Oregon Department of Forestry, said Friday at a news conference. He said fire officials were most concerned about 16 fires, some of which are likely to remain active until the heavy rains of late fall.

Grafe warned that the Riverside, Beachie Creek and Lionshead fires, which are burning east of Salem, are responsible for some of the state’s “most dramatic fire growth.”

“We have not seen the likes of this fire in this state integrated with our communities ever before,” he said.

As the Beachie Creek and Riverside fires continued to move closer to each other on Friday, Holly Krake, a spokeswoman for the U.S. Forest Service, told the Statesman Journal that the convergence of smoke plumes from the fires could cause erratic wind shifts and other weather events. She said those conditions would make it harder for firefighters to combat the blaze and heighten the risk for people in the fire’s path.

While the National Weather Service said air quality in the Portland area was expected to start gradually improving Friday after days of smoke, the situation there remained dire. Air quality monitoring website IQAir.com reported four of the five major cities worldwide with the most air pollution were on the western coast of North America: Portland, Ore., Seattle, Vancouver, B.C., and San Francisco.

In addition to the wildfires, Oregon officials also battled misinformation about the cause of the blazes. Several law enforcement agencies went on social media to dispel rumors that far-left or far-right antagonists had purposely caused some of the outbreaks.

“Rumors spread just like wildfire and now our 9-1-1 dispatchers and professional staff are being overrun with requests for information and inquiries on an UNTRUE rumor that 6 antifa members have been arrested for setting fires in DOUGLAS COUNTY, OREGON,” the Douglas County Sheriff’s Office said on Facebook.

The FBI weighed in, too: “Reports that extremists are setting wildfires in Oregon are untrue,” FBI Portland tweeted.

In Jackson County, where the fires have destroyed hundreds of homes and businesses, the county sheriff on Friday announced arson charges against a 41-year-old man in connection to at least one portion of the Almeda fire there.

As the plumes of smoke covering the Oregon sky blotted out the sun, communities throughout the state prepared for the pending disaster they had seen play out in southern cities such as Talent and Phoenix, where entire communities were destroyed.

Portland Mayor Ted Wheeler (D) issued an emergency order Thursday night to close city parks and other outdoor properties for the next two weeks. The Oregon Convention Center transformed into a shelter for as many as 400 evacuees, offering a socially distanced space operated by the Red Cross for those in need of food, supplies or a hot shower.

At an evacuation site only half an hour outside of Portland, Maria Juarez, 74, and her daughter Guadalupe Juarez, 30, sat in lawn chairs in the thick smoke in the parking lot of the Clackamas Town Center. The two women, who are both on dialysis, fled their homes in Estacada on Thursday as fire officials warned the blazes were inching closer to their town.

“I’ve lived in this country for three decades and I’ve never had something like this happen to me, in the street with no place to sleep,” Maria Juarez said, bundled under donated blankets.

Angel Fujiyoshi, who had evacuated to the convention center from Oregon City, told KPTV that she left behind almost everything except her grandmother’s remains to secure shelter 15 miles away.

“I was able to grab her ashes, but other than that, we had to leave everything else behind to save our own lives, basically,” Fujiyoshi told the outlet.

Clackamas County enacted a curfew Friday to keep people who are not working to save lives or property off the road at night, and officials there asked people who were not under urgent evacuation orders to delay travel so those in the most danger could leave the area.

At the Coffee Creek Correctional Facility in Wilsonville, also in Clackamas County, all 1,303 inmates were evacuated and moved to another prison as wildfires have threatened to merge, the Salem Statesman Journal reported. The move came after three other prisons around Salem, the state capital, evacuated in recent days.

In Molalla, Ore., located in Clackamas County about 30 miles south of Portland, police rolled through the streets to emphasize the mandatory evacuation order by repeating over the loudspeaker, “Evacuate now.” One of those who fled from Molalla was Michael Smelser, who joined his family and their puppy in gathering whatever they could take in their RV over to the Clackamas Town Center in Happy Valley.

Speaking to KPTV in the parking lot of the center, Smelser admitted it was difficult to sleep knowing there’s a good chance his family’s house, and everything they built together, had been reduced to ashes.

“You would want a big semi-truck to grab everything,” Smelser said. “We told [our daughter], ‘Grab the toys you don’t want to burn.’ It’s hard to do to your kid. Say, ‘Hey, grab the toys, if you leave them here, they could burn.’ It’s hard to do.”

Samantha Schmidt contributed to this report.