Search and rescue crews using dogs combed through neighbourhoods left in blackened ruins by massive wildfires burning across three states as US President Donald Trump said he would travel to California to see the devastation first-hand.

Flames have destroyed thousands of homes and a half dozen small towns in the latest outbreak of wildfires that have burned across the western United States this summer, scorching a landscape the size of New Jersey and killing at least 26 people since early August.

But after four days of hot, windy weather, the weekend brought calmer winds blowing inland from the Pacific Ocean, and cooler, moister conditions that helped crews make headway against blazes that had burned unchecked earlier in theweek.

At least six people have been killed this week in Oregon, according to the state's wildfire tracking website.

Governor Kate Brown has said that dozens of people remained missing across three counties.

In California, tens of thousands of firefighters were battling 28 major wildfires, according to the California Department of Forestry and Fire Protection.

Improving weather conditions had helped them gain a measure of containment over most of the blazes.

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The White House said Mr Trump will meet with California officials tomorrow.

His democratic opponent in the November election, Joe Biden, linked the wildfires to climate change, echoing comments made on Friday by California Governor Gavin Newsom.

"The debate is over around climate change. Just come to the state of California. Observe it with your own eyes," Mr Newsom said in a briefing live streamed from a charred mountainside near Oroville, California.

The Pacific Northwest has since Labor Day endured a string of fierce wildfires that have darkened the sky with thick smoke and ash, creating some of the world's worst air-quality levels and driving residents indoors.

The small mountain town of Paradise, California, nearly destroyed in 2018 by the deadliest wildfire in state history, posted the world's worst air quality index reading at 592,according to the Purple Air monitoring site, as two of the state's largest blazes burned on either side of it.

More than 4,000 homes and other structures have been incinerated in California alone over the past three weeks.

In southern Oregon, charred residential estates and trailer parks stretched for kilometres along Highway 99 south of Medford through the neighbouring communities of Phoenix and Talent.

Molalla, a logging community 40km south of downtown Portland, was an ash-covered ghost town after its more than 9,000 residents were told to evacuate, with only 30 refusing to leave, the city's fire department said.

Molalla was on the front line of an evacuation zone stretching north to within 4.8km of downtown Portland.

In Portland, the Multnomah County Sheriff chastised residents who had set up their own checkpoints to stop carsafter conspiracy theories spread on social media that members of Black Lives Matter or Antifa were lighting fires.

Local officials have called those assertions groundless.

"We are removing false claims that the wildfires in Oregon were started by certain groups," a Facebook spokesman said.

"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."