PORTLAND, Ore. — Massive clouds of smoke from the Pacific Northwest wildfires lingered over the region Sunday, posing serious health risks for millions of people and complicating firefighting efforts even as crews reported progress in slowing some of the blazes.

The air quality across Oregon was listed as “hazardous” or “very unhealthy” by state environmental officials, and a dense smoke advisory from the National Weather Service remained in effect for much of the state until late Sunday or at least noon local time on Monday. Oregon officials said Sunday evening that crews are struggling to contain more than 30 fires still raging across the state — one of them stretching more than 55 miles wide, part of a burned area larger than Rhode Island.

Similar warnings about smoke were in place from California to Washington state. In San Francisco, residents were advised to remain indoors and block air from seeping into their homes. In Seattle, the air quality index topped 200, the level considered “very unhealthy.”

“The sun doesn’t seem to rise or set. The sky gets a little bit brighter and a little bit darker and that’s how you know the day is starting or ending,” said Eileen Quigley, founder and executive director of the Clean Energy Transition Institute in Seattle.

The thick haze smothering the landscape has deepened the crisis brought on by the blazes, which officials have linked to at least 10 deaths in Oregon as dozens remain missing.

In many parts of the state, the air quality ranked among the worst in the world, as bad as Beijing’s 2013 bout of pollution that was widely branded the “airpocalypse.” The smoke made the air potentially life-threatening for people with respiratory problems to venture outside. Even indoors, some residents were left coughing and fighting for breath. Outside, in some places, residents said they could not see further than 50 yards.

There were some hopeful signs. The high-speed winds abated and smoke blocked sunlight, lowering temperatures to the low 50s, well below normal. There is a chance of rain on Tuesday.

But people were still suffering, and the forest still burning.

In Michael Warner’s home in the backwoods of Marion County, the smoke was so bad he had to wear a mask inside. Unaware of evacuation orders, he was walking down his street Friday night when a neighbor drove up and told him to get in the car. With only his dog and the clothes he was wearing, Warner let the neighbor drive him to an evacuation site at the Oregon State Fairgrounds, where he spent the night.

“My throat burns,” Warner said as he ambled around the site with his dog, his eyes swollen and watering.

Thomas Keyzers, 36, had hoped that he’d left behind the worst of the smoke when he, his wife and two children, ages 3 and 5, evacuated their home in Happy Valley. But the smoke followed them to Portland, even inside the hotel where they were staying.

He and his wife have been coughing constantly, and it’s getting worse each day. He’s worried about the health of his kids, he said. “It’s just like a 24-hour campfire,” he said. “You can only take so much of it.”

Officials and health experts urged residents to stay indoors unless absolutely necessary, keep doors and windows closed and use fans and air conditioners to keep air circulating in their homes.

Bridges, buildings and roadways were shrouded in an eerie gray fog. Visibility was a quarter-mile or less in some places, according to the National Weather Service, making it dangerous to drive and hindering firefighters.

“Our challenges remain reduced visibility, limiting our aerial reconnaissance, and rapidly changing fire conditions,” Clackamas County fire officials said in a statement Saturday.

The wildfires have displaced tens of thousands of people in what officials have called an unprecedented disaster. The death toll reported so far was likely to rise as emergency crews began sifting through the wreckage, officials said.

In California, record-shattering wildfires have charred more than 3.2 million acres and have been linked to 24 deaths since last month. Three of the top four California wildfires are burning now, according to the state. In Washington state, blazes have burned more than 665,000 acres of land and clogged the skies with smoke.

The fires come on top of the pandemic, which had already hobbled schools and businesses.

Large numbers of schools in Oregon announced they would be closed until further notice. Toya Fick, the Oregon executive director of the education group Stand for Children, said the organization has shifted much of its attention from school programs to doing “triage” for food security, housing assistance and other emergency needs of families and teachers. The group had secured $500 million in tax revenue marked for education, but with the pandemic all but $150 million has been diverted to other priorities.

President Trump is slated to visit California on Monday for a briefing with emergency officials. Aside from a Friday night tweet thanking responders for their work, the president has said little publicly about the blazes that have wiped out entire neighborhoods and towns and destroyed vast tracts of land.

At a speech in Nevada over the weekend, Trump blamed the fires on poor forest management and boasted about the United States leaving the international climate agreement. He made a similar remark at a rally in August, saying, “You’ve got to clean your floors, you’ve got to clean your forests.”

On Sunday, Sen. Jeff Merkley (D-Ore.) pushed back on Trump’s characterizations, telling ABC News’s “This Week” that the devastation was the result of a combination of ills, including rising temperatures caused by global climate change.

“It’s just a big and devastating lie,” Merkley said of Trump’s statements. “The Cascade snowpacks have gotten smaller. Our forests have gotten drier. Our ocean has gotten warmer and more acidic.” The changes, Merkley added, are the “consequences of a warming planet.”

“We need to have a president follow the science,” he said.

Los Angeles Mayor Eric Garcetti (D) also accused Trump of negligence in responding to the fires. In an interview with CNN, he suggested the president was reluctant to help California, Oregon and Washington because they have Democratic governors.

“Leadership at the very top needs to be stronger, earlier,” Garcetti said, alleging that Trump’s “blaming of blue states over red states” in how he handles natural disasters hurts the federal response.

“We need leadership that is equal across this country, instead of being partisan and divisive,” Garcetti said.

Democratic presidential nominee Joe Biden — who has sought to contrast his agenda with the president’s on environmental issues — will be speaking Monday about the fires and the link between “extreme weather events” and climate change, his campaign said. Sen. Kamala D. Harris (Calif.), his running mate, will travel to her home state for a meeting Tuesday with emergency personnel.

Police and social media companies have been trying to stamp out false allegations that anti-fascist activists had set the fires. Facebook on Saturday said it would take down erroneous posts with such allegations.

Some climate activists said that even if climate was one of a combination of factors contributing to the fires, that was still disheartening.

“It is most distressing that these impacts are happening so much faster than were predicted,” Quigley said. “We are seeing disruption we thought we would see a decade or more from now, which demonstrates how little we really understand about feedback loops.”

As the fires raged, emergency crews got some reprieve over the weekend as strong winds died down and cooler, moister weather moved in over some of the region.

The Riverside Fire in Clackamas County near Portland had blackened more than 132,000 acres as of Sunday morning, but officials said its growth had slowed. Evacuation warnings in Oregon City, Sandy and Canby were downgraded from Level 2 to Level 1, meaning the imminent risks were lower but that residents should be prepared to evacuate if the flames start encroaching again.

To the south, some evacuation orders for California’s deadly Northern Complex Fire were lifted Sunday, and the San Francisco Bay Area division of the National Weather Service was optimistic about air quality. “The smoke off the coast looks a little more diluted today,” it wrote on Twitter, saying winds will “greatly help clear us out in the coming days.”

Elsewhere, the weather showed signs of worsening.

In rural Jackson County, Ore., the National Weather Service issued a red flag warning for Sunday, with warm temperatures, low humidity and strong winds creating tinderbox conditions in the area along the state’s southern border. “This will help alleviate some of the smoke in the region, but will also increase fire danger,” the service said.

The South Obenchain Fire had burned roughly 30,000 acres in the central part of the county and was menacing several small towns, including Eagle Point and Butte Falls. Another active fire was burning near Medford, Ore., the county seat. Residents were under evacuation orders or warnings.

“Residents in these areas should continue to take precautions by keeping defensible space around their homes free of flammable materials, gutters clear etc.,” the National Weather Service said in a technical forecast discussion posted online. “If you don’t have a ‘go bag’ ready, now is a great time to prepare.”

Dry, windy conditions were also forecast in northeastern California and western Nevada, according to the National Weather Service.

In Portland, 23-year-old Blazedol Howard wore a respirator mask over his face as he walked through the deserted streets downtown to get breakfast at a 7-Eleven. He said he had recently flown into the city from Indiana to march in Black Lives Matter protests and could smell the smoke during the plane’s descent. As he stepped out of the airport, the air felt suffocating.

“I felt like I couldn’t breathe,” he said.

When Howard reached the 7-Eleven, it was already boarded up from the riots downtown, along with many businesses in the city. Across the state, other stores, coffee shops and restaurants — some of which had just recently reopened after closing for the pandemic — taped signs on their doors reading, “Closed due to the air quality.”

A few blocks from where Howard was, Christopher Murillo and his husband, Leo Cruz, braved the smoke to walk their three dogs and pick up coffee from Starbucks.

The smoke was “excruciating,” Murillo, 33, said. “It’s itchy, like a constant dry mouth, like wanting to hack up something and it’s all this white nasty stuff.”

They haven’t seen the sun for days, said Murillo, who grows organic produce and flowers with his husband. The skies are depressing, and the haze is inescapable — even at night, in their bedroom.

“It’s like trying to gasp for air while you’re drowning,” he said.

Hawkins and Mufson reported from Washington and Schmidt reported from Oregon. Paul Kane, Tom Hamburger and Hannah Knowles in Washington contributed to this report.