US President Donald Trump said he will meet emergency services in California on Monday as record fires that have killed 27 people smothered the West Coast in dense smog.
Officials warned of further fatalities with swathes of land in California, Oregon and Washington still cut off by flames fueled by tinder-dry conditions, as presidential challenger Joe Biden linked the fires to climate change.
The unprecedented infernos have now burnt through nearly 5 million acres (2 million hectares), an area roughly the size of New Jersey.
Trump plans to meet with the heads of California's emergency services, battling fires that have scorched more than 3.2 million acres in the state this year -- an annual record, with nearly four months of fire season still to come.
He has made little comment about the blazes in recent weeks, but at a Nevada campaign event on Saturday he acknowledged the scope of the disaster.
"They never had anything like this," Trump said. "Please remember the words, very simple, forest management."
But Biden, speaking earlier, said the causes were much broader: "The science is clear, and deadly signs like these are unmistakable -- climate change poses an imminent, existential threat to our way of life."
"President Trump can try to deny that reality, but the facts are undeniable."
Worsening the sense of environmental catastrophe, all five of the world's most air-polluted cities Saturday were on the West Coast, according to IQAir, with dense smog and ash coating the atmosphere from Los Angeles up to Vancouver in Canada.
In Portland, thick, choking smoke blanketed the downtown area Saturday morning.
"It is as if I had smoked 100 cigarettes. I've never seen this but we try to stay positive as conditions are getting better," said a 37-year-old man who gave his name as Jessie.
'Dropped out of the sky'
More than 20,000 firefighters are battling the blazes, with officials warning that a respite provided by the arrival of cooler weather could end Monday as warmer, drier conditions return.
Oregon has suffered another four deaths in the past 24 hours, bringing the state's death toll this week alone to 19.
Among them was a 13-year-old boy found in a car with his dog in his lap in Oregon. The road was so hot it had melted the tires as he tried to flee.
Emergency official Andrew Phelps warned Oregon is "preparing for a mass fatality incident based on what we know and the number of structures that have been lost."
Preparations have been hampered by online claims that "extremists" are intentionally setting fires in Oregon, which have been debunked by the FBI.
Facebook said Saturday it was removing the posts, some of which sought to link the blazes to Antifa -- a structureless movement that says it is dedicated to fighting fascism and is a favored target of conservatives.
"This is based on confirmation from law enforcement that these rumors are forcing local fire and police agencies to divert resources from fighting the fires and protecting the public," wrote Facebook spokesman Andy Stone.
In Estacada, a rural Oregon town just miles from the fire, that was deserted earlier this week, some inhabitants returned from evacuation Saturday and patrolled the streets with guns for fear of looting, according to an AFP reporter.
Others holed up indoors as thick acrid smoke hung in the air and fresh layers of ash from nearby blazes continued to blanket the streets.
Police in Multnomah County, where Portland is situated, issued a notice threatening arrest to armed residents who had established roadblocks near their communities.
Joy, a 56-year-old woman sheltering outside Portland who declined to give her last name, told AFP that she and her daughter don't know if their house in Aims -- a short drive east -- is still standing.
"We saw a bird that was flying and then all sudden it just completely dropped out of the sky... if it's killing God's creatures, I don't want to die too. So we left," she told AFP.
In California, Butte County sheriff Kory Honea said additional officials had been brought in to check for human remains, but "right now, the areas that we need to search are too hot."
In a rare sliver of good news, one believed fire victim in Butte County turned out to be a burned anatomical skeleton from a local classroom.