SHAVER LAKE, CALIF. -- Wildfires have burned a record 2 million acres in California this year, and the danger for more destruction is so high the U.S. Forest Service announced Monday it was closing all eight national forests in the southern half of the state.

After a typically dry summer, California is parched heading into fall and what normally is the most dangerous time for wildfires. Two of the three largest fires in state history are burning in the San Francisco Bay Area. More than 14,000 firefighters are battling those fires and dozens of others more around California.

A three-day heat wave brought triple-digit temperatures to much of the state during Labor Day weekend. But right behind it was a weather system with dry winds that could fan fires. The state's largest utility, Pacific Gas & Electric, was preparing to cut power to 158,000 customers in 21 counties in the northern half of the state to reduce the possibility its lines and other equipment could spark new fires.

Randy Moore, regional forester for the Forest Service's Pacific Southwest Region that covers California, announced the national forest closures and said the decision would be re-evaluated daily. Campgrounds at all national forests in the state also were closed.

"The wildfire situation throughout California is dangerous and must be taken seriously." Moore said. "Existing fires are displaying extreme fire behaviour, new fire starts are likely, weather conditions are worsening, and we simply do not have enough resources to fully fight and contain every fire."

Lynne Tolmachoff, spokeswoman for the California Department of Forestry and Fire Protection, or Cal Fire, said it's "unnerving" to have reached a record for acreage burned when September and October usually are the worst for fires because vegetation has dried out and high winds are more common. The previous high was 1.96 million acres burned in 2018. Cal Fire began tracking the numbers in 1987.

While the two mammoth Bay Area fires were largely contained after burning for three weeks, firefighters struggled to corral several other major blazes ahead of the expected winds. Evacuation orders were expanded to more mountain communities Monday as the largest blaze, the Creek Fire, churned through the Sierra National Forest in Central California.

It was one of many recent major fires that has displayed terrifyingly swift movement. The fire moved 15 miles (24 kilometres) in a single day and burned 56 square miles (145.04 square kilometres).

Debra Rios wasn't home when the order came to evacuate her hometown of Auberry, just northeast of Fresno. Sheriff's deputies went to her ranch property to pick up her 92-year-old mother, Shirley MacLean. They reunited at an evacuation centre.

"I hope like heck the fire doesn't reach my little ranch," Rios said. "It's not looking good right now. It's an awfully big fire."

Mountain roads saw a steady stream of cars and trucks leaving the community of about 2,300 on Monday afternoon.

Firefighters working in steep terrain saved the tiny town of Shaver Lake from flames that roared down hillsides toward a marina. About 30 houses were destroyed in the remote hamlet of Big Creek, resident Toby Wait said.

"About half the private homes in town burned down," he said. "Words cannot even begin to describe the devastation of this community."

A school, church, library, historic general store and a major hydroelectric plant were spared in the community of about 200 residents, Wait told the Fresno Bee.

Sheriff's deputies went door to door to make sure residents were complying with orders to leave. Officials hoped to keep the fire from pushing west toward Yosemite National Park.

The Creek Fire had charred more than 114 square miles (295 square kilometres) of timber after breaking out Friday. The nearly 1,000 firefighters on the scene had yet to get any containment. The cause had not been determined.

On Saturday, National Guard rescuers in two military helicopters airlifted 214 people to safety after flames trapped them in a wooded camping area near Mammoth Pool Reservoir. Two people were seriously injured and were among 12 hospitalized.

On Monday night, a military helicopter landed near Lake Edison to rescue people trapped by the Creek Fire, the Fresno Fire Department said on Twitter.

Chief Warrant Officer Joseph Rosamond, the pilot of a Chinook helicopter, said visibility was poor and winds increasingly strong during the three flights he made into the fire zone. His crew relied on night-vision goggles to search for a landing spot near a boat launch where flames came within 50 feet (15.24 metres) of the aircraft.

The injured, along with women and children, took priority on the first airlift, which filled both helicopters to capacity, he said.

"We started getting information about how many people were out there, how many people to expect, and that number kept growing. So we knew that it was a dire situation," Rosamond said.

Rosamond called the conditions "extreme" and said it was one of the most difficult flying missions in his 25 years as a military pilot.

Record-breaking temperatures were driving the highest power use of the year, and transmission losses because of wildfires have cut into supplies. Throughout the holiday weekend, the California Independent System Operator that manages the state's power grid warned of outages if residents didn't reduce their electricity usage. But none had occurred by late Monday afternoon.

Pacific Gas & Electric warned it might cut power starting late Monday because of the increased fire danger. Some of the state's largest and deadliest fires in recent years have been sparked by downed power lines and other utility equipment.

PG&E received criticism for its handling of planned outages last year. The utility said it has learned from past problems, "and this year will be making events smaller in size, shorter in length and smarter for customers."

In Southern California, crews scrambled to douse several fires that roared to life in searing temperatures, including one that closed mountain roads in Angeles National Forest and forced the evacuation of the historic Mount Wilson Observatory. Late Monday night, the Los Angeles County Fire Department told residents of Duarte, Bradbury and Monrovia near the forest to get ready for the possibility of evacuating.

Cal Fire said a blaze in San Bernardino County called the El Dorado Fire started Saturday morning and was caused by a smoke-generating pyrotechnic device used by a couple to reveal their baby's gender. In eastern San Diego County, a fire destroyed at least 10 structures after burning 16 square miles (41.44 square kilometres) and prompting evacuations near the remote community of Alpine in the Cleveland National Forest.

California has seen 900 wildfires since Aug. 15, many of them started by an intense series of thousands of lightning strikes in mid-August. There have been eight fire deaths and more than 3,300 structures destroyed.

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Weber reported from Los Angeles.