CASTAIC, Calif. —California wildfires erupted Wednesday in rural areas, racing through bone-dry brush and prompting evacuations as the state sweltered under a heat wave that could last through Labor Day.

Gov. Gavin Newsom declared a state of emergency with temperatures expected to be 10 to 20 degrees above normal, and urged people to help reduce demand for electricity by turning their thermostats up to 85 degrees if they won't be at home over the holiday weekend.

The Route Fire in Castaic in northwestern Los Angeles County raged through about 4,625 acres of hills containing scattered houses. Interstate 5, a major north-south route, was closed by a blaze that burned several hundred acres in only a few hours.

Media reports showed a wall of flames advancing uphill and smoke billowing thousands of feet into the air while planes dumped water from nearby Castaic Lake. There were no immediate reports of damage to buildings but a mobile home park with 94 residences was evacuated.

An elementary school also was evacuated. Temperatures in the area hit 107 degrees and winds gusted to 17 mph, forecasters said.

Eight firefighters were treated for heat-related problems, including six who were sent to hospitals, but all were in good condition, Los Angeles County Fire Department Deputy Chief Thomas Ewald said.

More injuries were expected as crews cope with extreme heat that was expected to stretch into next week, Ewald said during a news conference Wednesday night.

"Wearing heavy firefighting gear, carrying packs, dragging hose, swinging tools, the folks out there are just taking a beating," he said.

Aircraft would continue to drop water and fire retardant on the blaze overnight and winds could shift to the north through the night, causing the fire to burn back on itself, Ewald said.

Ewald also said there could be other fires in LA County as the searing heat continues. Bulldozers to cut firebreaks will be staffed around the county Thursday as a precaution, he said.

"This is the fire that's burning right now. But we have 4,000 square miles of LA County that we have to consider for tomorrow," he said.

Another fire burned at least four buildings, including a home, and prompted evacuations in the Dulzura area in eastern San Diego County near the Mexican border. It swiftly grew to more than 1,600 acres acres and prompted evacuation orders for at least 400 homes, authorities said.

State Route 94 was closed. The Mountain Empire Unified School District will be closed Thursday, officials said.

U.S. Customs and Border Protection announced that the Tecate port of entry with Mexico closed three hours early on Wednesday night because of the fire and wouldn't reopen until conditions improved to ensure "the safety of the traveling public." Travelers could continue to use the 24-hour Otay Mesa crossing.

No injuries were immediately reported, but there were "multiple close calls" as residents rushed to flee, said Capt. Thomas Shoots with the California Department of Forestry and Fire Protection.

"We had multiple 911 calls from folks unable to evacuate" because their homes were surrounded by the fire, Shoots told the San Diego Union-Tribune.

The National Weather Service said many valleys, foothills, mountains and desert areas of the state remained under an elevated fire risk because of low humidity and high temperatures, which set several records for the day. The hottest days were expected to be Sunday and Monday.

Wildfires have sprung up this summer throughout the Western states. The largest and deadliest blaze in California this year erupted in late July in Siskyou County, near the Oregon state line. It killed four people and destroyed much of the small community of Klamath River.

Scientists have said climate change has made the West warmer and drier over the last three decades and will continue to make weather more extreme and wildfires more frequent and destructive. Across the American West, a 22-year megadrought deepened so much in 2021 that the region is now in the driest spell in at least 1,200 years.