Oroville, September 10: A Northern California wildfire burning for more than three weeks roared to life after being stoked by high winds, spreading at a ferocious rate across an estimated 40 kilometres of mountainous terrain and parched foothills and destroying an untold number of homes.

As thick smoke choked the air on Wednesday and cast an eerie orange hue across much of the region, thousands of people in communities near Oroville were ordered to evacuate. The fire even threatened the town of Paradise that was devastated just two years ago by the deadliest blaze in state history, causing a panic that led to a traffic jam as residents tried to escape.

Daniel Swain, a climate scientist at the University of California, Los Angeles, said the fire had conservatively burned about 1,036 square kilometers in 24 hours. "The unbelievable rates of spread now being observed on these fires — it is historically unprecedented," Swain tweeted. California Wildfires: Smoke Turns Skies Orange, Barack Obama Says 'Protecting Our Planet is on the Ballot, Vote like Your Life Depends on It'; View Pics.

The North Complex fire was one of more than two dozen in the state, including three of five largest ever as wildfires burned across parts of the West amid gusty, dry conditions. Forecasters said some weather relief was in sight that could help firefighters overwhelmed by the blazes.

In Washington, more acres burned in a single day than firefighters usually see all year. Fires also forced people to flee homes in Oregon and Idaho. A blast of polar air helped slow wildfires in Colorado and Montana.

Since the middle of August, fires in California have killed eight people, destroyed more than 3,600 structures, burned old growth redwoods, charred chaparral and forced evacuations in communities near the coast, in wine country and along the Sierra Nevada.

The US Forest Service, which had taken the unprecedented measure of closing eight national forests in Southern California earlier in the week, ordered all 18 of its forests in the state closed on Wednesday for public safety.

The fire raging outside Oroville, 200 kilometres northeast of San Francisco, was burning in the Plumas National Forest after a series of wildfires sparked August 17 by lightning had merged.

The fire jumped the middle fork of the Feather River on Tuesday and, driven by 72 kmph winds, leapt into a canopy of pines and burned all the way to Lake Oroville -- about 40 kilometres -- said Jake Cagle, one of the fire chiefs involved.

The fire had been 160 square kilometres and 50 per cent contained before it grew more than sixfold. Firefighters were focused on saving lives and homes instead of trying to halt the fire's advance, Cagle said.

The fire tore into several hamlets along the river and near Lake Oroville, levelling countless homes and other buildings, said Daniel Berlant, a spokesman with the California Department of Forestry and Fire Protection.

"We know that the fire was burning incredibly rapidly into Berry Creek and did do a lot of destruction," Berlant said. A massive cloud of smoke covered much of California, darkening morning skies and later casting a sunsetlike glow over the northern part of the state.

In Paradise, where 85 people lost their lives and nearly 19,000 buildings were destroyed, the sky turned from black to cherry red and ash carried on strong winds rained down in a scene reminiscent from the fateful morning of November 8, 2018, former Mayor Steve "Woody" Culleton said.

"It was extremely frightening and ugly," Culleton said. "Everybody has PTSD and what not, so it triggered everybody and caused terror and panic." A power shutoff to prevent electric lines from sparking wildfires -- the cause of the Paradise fire -- prevented people from getting up-to-date information by internet, TV or their home phones, Culleton said.

Many of the residents decided to leave and created a traffic jam leading out of town, another scary reminder of the bottleneck where several residents died two years ago.

In Southern California, fires burned in Los Angeles, San Bernardino and San Diego counties. People in foothill communities east of Los Angeles were warned to be ready to flee, but the region's notorious Santa Ana winds were weaker than predicted.

"We're encouraged that the wind activity appears to be dying down," Governor Gavin Newsom said. "The rest of the week looks a little more favourable." Three firefighters injured along the Central Coast on Tuesday when they were overrun trying to protect a mountaintop fire station above Big Sur were expected to make full recoveries and could be discharged by the end of the week, Los Padres National Forest spokesman Andrew Madsen said.

The injured firefighters and 11 others had to deploy emergency fire shelters -- a last ditch safety measure -- when winds unexpectedly shifted, Madsen said.

"It's a really harrowing experience for those who go through a close encounter like that and we're very grateful that the injuries are such that all three who were hospitalised are going to recover and return to work," he said.

That fire, which had doubled overnight Tuesday and burned terrain that hadn't seen fire in 40 years, destroyed an office, two fire engines, barracks and all the firefighters' personal belongings inside. El Dorado Fire: Women Who 'Invented' Gender Reveal Parties Asks People to 'Stop Having These Stupid Parties, No One Cares' Following the Recent Disaster in California.

California has set a record with nearly 2.5 million acres burned already this year, and historically the worst of the wildfire season doesn't begin until fall.

Pacific Gas & Electric was deploying more than 3,000 employees on Wednesday to inspect power lines before restoring energy to about 167,000 customers whose electricity was turned off to prevent fires from being started by wind-damaged wires.

Some aerial inspections were paused because of smoke limiting visibility, said spokesman Jeff Smith. Only a very small number of customers had power turned off in Southern California.

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