A firefighter cut defensive lines and light backfires to protect structures behind a fire station during the Bear fire, part of the North Lightning Complex fires in the Berry Creek area of unincorporated Butte County, California on Wednesday. Photo: AFP

Hundreds of homes including entire communities were razed by wildfires in the western US Wednesday, as officials warned of potential mass deaths under apocalyptic orange skies.

At least six people have been killed in the fires, with officials warning that more deaths would likely be reported in the next few days as many areas are impossible to reach.

In Oregon, at least five towns were "substantially destroyed" as widespread evacuations took place across the northwestern state, Governor Kate Brown said.

"This could be the greatest loss of human lives and property due to wildfire in our state's history," she told a press conference.

Neighboring California and Washington states have been scrambling to contain rapidly spreading wildfires since the weekend due to unprecedented heatwaves followed by intense, dry winds.

Fatalities on Wednesday included a 1-year-old baby boy who perished while his parents suffered severe burns as they attempted to flee an inferno 209 kilometers east of Seattle, in Washington state.

Three unidentified people were killed in northern California, while two more deaths were confirmed in the Santiam Canyon region, 96 kilometers south of Portland, Oregon.

"They are not going to be the only folks that we find deceased up there [in Santiam]," said Marion County sheriff Joe Kast. 

Jody Evans, a resident of Detroit - one of the five towns devastated in Oregon - fled her home as the fire approached.

"Coming through fire on both sides, trees down, wind blowing, ash flying," Evans told Newschannel 21. "It was like driving through hell."

Sandra Spelliscy, city manager of Talent, Oregon, told AFP that only "smoldering ruins" remained of large parts of her community.

"There are numerous neighborhoods where there are no structures left standing... dozens of homes [gone] and literally nothing except the skeletons of a chimney or an appliance, a water heater," she said.

In California, people in the San Francisco Bay Area awoke to a deep orange sky caused by wildfire smoke that at times blocked out sunlight entirely.

Photos of the eerie scene, particularly of a San Francisco skyline fit for a dystopian science fiction film, spread quickly on social media.

"We know the smoke, darkness, and orange glow is scary. Stay calm and try to stay indoors," tweeted the fire department.

Cars crossing the famous Golden Gate Bridge were forced to switch their lights on throughout the day.

At the Creek Fire in central California, exhausted firefighters raced between blazes as thick columns of smoke rose up from the Sierra forest - now closed, along with all 18 of the state's national forests.

In one home near Shaver Lake, only the scorched remains of a washing machine, outdoor dining table and chairs were left standing beside the ash-coated chassis of a pickup truck, according to an AFP reporter.

"It's scary... we just left everything," said 68-year-old Sandy Clark, who fled her home for a hotel rather than a crowded shelter due to coronavirus fears.

Tens of thousands of people have been forced to evacuate homes across the region.

In Washington, where the town of Malden was decimated, Governor Jay Inslee described the wildfires as "unprecedented and heartbreaking."

"We're living in a new world - this is not the old Washington," he said.

"The devastation is all over our state."