Falling temperatures continued to provide a valuable boost to firefighters battling the Airport Fire burning in Orange and Riverside counties Thursday, with crews finally beginning to establish containment lines while again slowing the spread of the blaze.

As of Thursday evening, the fire was estimated at 23,410 acres, with 5% containment.

Orange County Fire Authority Capt. Steve Concialdi said about 770 firefighters were battling the blaze "and more are coming to assist."

"This marine layer and cooler temperatures along with the higher relative humidity are helping firefighters grow our containment fires and extinguish hot spots," Concialdi said Thursday morning. "Unfortunately, due to the marine layer helicopters were unable to fly last night, but starting this morning our firefighters are improving those containment lines and going into those burn areas and extinguishing hot spots."

"We are constructing a large dozer containment line from below the fire, starting in Robinson Ranch and behind the communities of Dover Canyon and Coto de Caza all the way to Ortega Highway just in case we have any wind shift or if the Santa Ana winds develop at some point," Concialdi said. "This will be a barrier and will slow the fire and keep the fire away from those communities."

Firefighters were reinforcing containment lines southwest of the fire. A flare-up occurred in an unburned pocket north of Trabuco Canyon, but it remained within the fire's existing perimeter. Crews were conducting reconnaissance along the Santiago Peak fire lines, and heavy equipment operators were constructing a dozer line toward the Ortega highway.

Aircraft such as Air Tankers and helicopters were utilized throughout the afternoon.

At a Wednesday afternoon news conference, OCFA Division Chief Kevin Fetterman reported two civilian injuries -- one who suffered a medical emergency and one with unspecified burns -- and a total of 10 firefighter injuries.

Concialdi said earlier Wednesday most of those firefighter injuries were heat-related, "but one did get stung by numerous bees, and one sustained minor burns and the other couple had some injuries from fighting the fire, but all were released from the hospital and are doing well."

The end of the Southland's prolonged heat wave began assisting in the firefight Tuesday night, Concialdi said. Burn scars from the Holy Fire in 2018 and 2022 also provided much-needed breaks in the fuel feeding the blaze.

Officials were reporting two structures destroyed and six more damaged.

"We can confirm that there were some homes damaged and destroyed in the communities around Ortega Highway," but details were still being collected, Concialdi said.

As of Wednesday, the Orange County Fair and Event Center had taken in 93 horses evacuated due to the fire.

On Tuesday, the Orange County Board of Supervisors approved an emergency declaration in response to the fire, in hopes of obtaining additional financial resources for the firefight and eventual recovery. Meanwhile, Gov. Gavin Newsom secured assistance from the Federal Emergency Management Agency for all the fires in the state, including the Airport Fire, the Bridge Fire burning in Los Angeles and San Bernardino counties and the Line Fire in San Bernardino County.

The Airport Fire began about 1 p.m. Monday near Trabuco Canyon Road in the area of the remote-controlled airplane airport, said Orange County Fire Authority Capt. Sean Doran. By Tuesday morning, the fire had raced up the canyons and hillsides and crested into Riverside County, burning toward the El Cariso and Lake Elsinore areas, where evacuation warnings and orders were in place.

In Orange County, evacuation orders were in place as of Thursday evening in the areas of Ortega Highway, Caspers Park, Blue Jay Campground and El Cariso.

Evacuation warnings were issued for Robinson Ranch, Rose Canyon, Trabuco Canyon, Dove Canyon, Silverado Canyon, Modjeska Canyon and East Side Coto de Caza.

Evacuation warnings were issued for a host of Riverside County areas near the fire zone, generally in an area east of the Orange County line, north of the San Diego County line, south of Bedford Motor Way and west of Interstate 15.

Early Tuesday afternoon, some of those warnings became evacuation orders, impacting an area generally north of the San Diego County line, east of the Orange County line, south of Lake Elsinore near the base of Ortega Highway and west of South Main Divide Road/Grand Avenue.

On Thursday afternoon, with conditions easing, mandatory evacuations were reduced to evacuation warnings in some neighborhoods:

Residents can visit go.genasys.com/11hh53 to determine if their homes are impacted by evacuation orders or warnings.

Ortega Highway was closed east of Quarry to Grand Avenue in Lake Elsinore. That area had been under a voluntary evacuation warning, but late Tuesday morning, mandatory evacuation orders were issued for areas along the highway near Caspers Park.

In Orange County, an evacuation center was established at RSM Bell Tower Community Center, 22232 El Paseo in Rancho Santa Margarita.

Large animals were being housed at Orange County Fairgrounds, Los Alamitos Race Course and Nohl Ranch Saddle Club at 6352 E. Nohl Ranch Road in Anaheim.

Orange County Fire Authority Deputy Chief TJ McGovern told reporters Monday night that the fire was accidentally sparked by a county work crew. McGovern said Orange County Public Works crews were working in the area near Trabuco Creek Road, using heavy equipment to place boulders meant to replace barriers used to restrict access to the vegetation.

The OCFA was using new firefighting helicopters that can dump 1,000 gallons of water on the flames, Doran said.

Robinson and Trabuco Elementary schools in the Saddleback Valley Unified School District in Orange County were also closed Tuesday and Wednesday, and remained closed Thursday. Santa Margarita Catholic High School reopened Thursday on a limited schedule, but will close again Friday for a previously scheduled teacher convocation event.

The Airport Fire was one of three large wildfires burning in Southern California this week. The Line Fire had burned 37,589 acres in San Bernardino County by Thursday evening and was 21% contained, while the Bridge Fire in Los Angeles and San Bernardino counties had burned 51,580 acres and was at 0% containment.

The South Coast Air Quality Management District extended an air quality advisory until at least 11 p.m. Friday for Los Angeles, Orange and Riverside counties due to smoke from all three wildfires.