Helicopters drop water on the Route Fire in Castaic, California, Wednesday.
CNN  — 

After a wildfire raging in Los Angeles County swelled to more than 5,200 acres in less than 48 hours, a top fire official warned the explosive growth should be a “wake-up call” to residents.

The Route Fire began Wednesday around noon near Castaic Lake and grew so quickly that a portion of Interstate 5 was shut down in both directions.

“The fire behavior and what you saw yesterday should be a wake-up call to us all about the potential that we’re in and we’re entering into over the next few days in terms of the fire conditions, very rapid fire growth, and very, very explosive fire behavior,” said Angeles National Forest Chief Robert Garcia.

As of Thursday night, the wildfire was about 27% contained, according to California’s wildfire tracking website. I-5 was reopened Thursday afternoon in both directions, though some lanes remain shut down, according to the state’s transportation department.

Several evacuation orders were issued Wednesday, though all were lifted by Thursday evening.

The blaze erupted as the region was in the grips of a blistering heat wave which led California Gov. Gavin Newsom to issue a state of emergency. Officials have urged residents to lower their electricity use during peak hours to avoid straining the power grid.

Residents who were evacuated from their home watch as the Route Fire burns on August 31, 2022 near Castaic, California.

“This will be the longest and most intense heat streak so far this calendar year,” Alexis Clouser from the National Weather Service in San Francisco told CNN.

Crews prepare for more heat-related health emergencies

Amid the sweltering heat, fire crews focused on “boxing the fire in, reinforcing our fire lines and then anticipating some fire development” due to the high afternoon temperatures, LA County Fire Deputy Chief Thomas Ewald said in the news conference Thursday.

The stifling temperatures were top of mind for officials as they worked to contain the fire but also preserve the safety of those fighting it.

Seven firefighters suffered heat-related injuries Wednesday, the Los Angeles Fire Department said on social media. Several were hospitalized and have since been released, Ewald said, adding that crews are preparing for more heat-related health emergencies in the days ahead.

Temperatures hit triple digits in some areas of California on Thursday amid the intense heat streak, according to the weather service.

Officials have not disclosed the cause of the fire as it remains under investigation.

Two structures were destroyed in the fire and 550 were threatened, according to the fire department.

More that 500 fire personnel have been deployed to contain the fire, along with 58 fire engines, 8 helicopters and two fixed-wing planes, according to the fire department.

But fires burning elsewhere in the state are forcing officials to split resources, Ewald said.

“There’s a large fire burning on the border down in San Diego County, and so those (fixed-wing) aircraft are being pulled off of these fires,” he said. “There’s homes being lost in that area and so the priorities shift throughout the day. … We ordered more fixed wing but some of those aircraft are being diverted to that fire.”

Ewald appeared to be referring to the Border 32 fire, which has consumed 4,438 acres along the US-Mexico border near the Mexican city of Tecate. It is only 14% contained, according to the state’s wildfire tracking website.

Mill Fire breaks out in Northern California

Another fire ignited early Friday afternoon, sending huge plumes of smoke billowing out of Weed, California.

The Mill Fire is currently at 900 acres and 0% containment as of 3:55 p.m., and evacuations are in place, CAL Fire Public Information Officer Susie Brady told CNN.

Evacuation orders have also been issued in Lake Shastina and Edgewood, according to the Siskiyou County Sheriff’s Office.

The fire is located about 60 miles away from the McKinney Fire, which started in late July and burned more than 60,000 acres, destroying nearly 185 structures, including 90 residences.

There are some civilian injuries, although it is unclear how many, Brady said. People were treated on the scene and sent to a hospital, according to Brady.

Multiples structures have been destroyed, but Brady did not have a firm number. The Roseburg Forest Products Mill was one of the first buildings to ignite, but it is not the cause of the fire, Brady said, adding the cause is currently under investigation.

CNN’s Elizabeth Wolfe, Taylor Romine, and Stella Chan contributed to this report.