More than 20,000 firefighters from across the United States on Friday battled sprawling deadly wildfires up and down the West Coast — a wave of infernos that have forced more than half a million people to flee their homes.

The true scale of destruction was hard to gauge, with 16 deaths confirmed so far this week as wide stretches of California, Oregon and Washington remain cut off by flames.

The biggest recorded blaze in Californian history — the August Complex Fire — has ripped through 746,000 acres (302,000 hectares) of dry vegetation in the state’s north, as multiple fires combined under high temperatures and strong, dry winds.

But it is just one of around 100 large fires on the US West Coast, and other rapidly growing blazes closer to populated areas have proven more deadly.

So far, 10 people have been confirmed dead in northern California’s Butte County.

“We are at a complete loss for words right now,” Bobbie Zedaker told the San Francisco Chronicle, after DNA tests proved her missing 16-year-old nephew Josiah Williams was among those killed.

Two more people were killed near the rural community of Happy Camp, a Cal Fire spokeswoman told AFP Friday.

In neighboring Oregon, half a million people have been evacuated.

Two massive conflagrations threatened to merge south of Portland in Clackamas County, where a 10:00 pm curfew was announced for all non-emergency workers to clear the roads for patrol and evacuation efforts.

Portland’s mayor declared a state of emergency late Thursday.

Governor Kate Brown said the area incinerated in just 72 hours was twice the state’s annual average, and at least five towns had been “substantially destroyed.”

“We have never seen this amount of uncontained fire across our state,” she told a press conference.

Huge wildfires are becoming more common, with the World Meteorological Organization saying the five years to 2019 was unprecedented for fires, especially in Europe and North America.

Butte county firefighters watch as flames tower over their truck at the Bear fire in Oroville, California.

Climate change amplifies droughts which dry out regions, creating ideal conditions for wildfires to spread out of control and inflict unprecedented material and environmental damage.

‘Leave your house’

Oregon officials confirmed two deaths in the Santiam Canyon region south of Portland, and a third near the California border.

Police went door to door to make sure that residents were evacuating the city of Molalla, marking their driveways with spray paint to show they had left.

“It’s one thing to leave your house, it’s another thing being told that you have to leave,” said Denise Pentz, a resident of the town for 11 years, who was loading her family belongings into a camping trailer.

In Washington state, a one-year-old boy perished while his parents suffered severe burns as they attempted to flee an inferno 130 miles (210 kilometres) east of Seattle.

“This child’s family and community will never be the same,” said governor Jay Inslee.

‘Glowing red’

Winds that whipped up flames earlier in the week have eased off across much of California, with severe weather warnings lifted for most of the state by Friday.

Humidity is expected to rise as temperatures cool through to next week, providing some relief, Cal Fire said.

But California has already seen more than 3.1 million acres burn this year — an annual record, larger than the entire state of Connecticut — with nearly four months of fire season still to come.

Tina Rose, 29, who fled her home in central California, described witnessing a nearby mountain “glowing red” from looming wildfires.

“It is something we never want to experience again,” she told AFP, speaking from her brother-in-law’s crowded home near Fresno.

Eight more people were killed in California wildfires last month.

(Source: AFP)