A house is engulfed in flames during the Valley fire in Seigler Springs, California on September 13, 2015
Los Angeles (AFP) - A state of emergency has been declared as raging wildfires spread in the northern part of drought-ridden California, possibly killing one person and forcing thousands to flee the flames.
More than 5,500 firefighters are struggling to contain the monster blazes that have charred more than 100,000 acres (40,470 hectares), authorities said, destroying hundreds of homes and commercial structures.
"There is a report of a fatality on the #ValleyFire," CAL FIRE spokesman Daniel Berlant said on Twitter, adding that the information was being confirmed with the sheriff's office.
Four firefighters suffered second-degree burns while battling the blaze, and are being treated in hospital.
Eight major fires are currently burning but two -- the Valley Fire about 100 miles (160 kilometers) west of the state capital Sacramento and the Butte Fire about 100 miles to the east -- have been particularly damaging over the last week, with little let-up in sight.
Driven by dry conditions, high winds and soaring temperatures, the Butte Fire has burned 65,300 acres and was just 25 percent contained, while the Valley Fire had grown to 50,000 acres and was zero percent contained, state fire agency CAL FIRE said late Sunday.
The Valley Fire has destroyed about 400 homes and other structures and the Butte Fire some 135 homes, 79 outbuildings and four other structures.
They have also destroyed or forced the closure of highways.
"My heart goes out to all those who lost homes and businesses in the devastating fires in California," Senator Barbara Boxer said in a tweet.
"Praying for the safety of all."
Governor Jerry Brown issued an emergency proclamation for Lake and Napa counties -- wine-producing regions north of San Francisco -- due to the massive Valley Fire. Schools in the counties were scheduled to be closed Monday.
About 6,400 homes are still threatened by these monster fires, according to Berlant, though some evacuation orders linked to the Butte fire have been lifted.
Three other fires are scorching the earth in neighboring Oregon state and 10 further north in Washington state.
Nearly 70 firefighters from Australia and New Zealand are assisting fire services in the western United States.
- Costs soar, air quality drops -
A record drought that began four years ago is worsening the situation.
Berlant said that CAL FIRE has so far spent more than $212 million since July 1 to fight fires under its jurisdiction and that approximately 5,000 firefighters were currently assigned to major blazes.
The costs of containing other fires, such as those blazing in Sierra Nevada forests, are largely covered by federal agencies and not included in those figures.
The US Forest Service has spent an additional $1.31 billion battling fires and says it is approaching its record expenditure, from 2002, of $1.65 billion.
Brown's state of emergency will release additional funds to cover the costs of the firefighting efforts.
National Guard troops have also been called in to help.
After a briefing on the Butte blaze, the governor's emergency services chief said this summer's fires were the most volatile he had ever seen.
"The fires are spreading faster than I have seen in my 30 years," Mark Ghilarducci was quoted as saying by The Sacramento Bee newspaper.
Meanwhile, the state's air quality has also taken a hit from the fires.
"As a result of the Valley Fire, combined with the drought conditions and other wildfires burning in the state, California's air quality has significantly deteriorated," the governor said in his emergency declaration.