SAN DIEGO (AP) -- More wildfires broke out Wednesday in San Diego County -- threatening homes in Carlsbad and forcing the evacuations of military housing and an elementary school at Camp Pendleton -- as Southern California is in the grip of a heat wave.

Wind-driven flames began raging Wednesday morning on the Marine Corps' Camp Pendleton and to the south in the coastal city of Carlsbad. A third fire spread from a burning vehicle on coastal Interstate 5 to roadside brush near the northwest corner of the Marine base.

Earlier, authorities reported 25 percent containment of a 2.42-square-mile fire that broke out Tuesday and forced thousands of people to flee the Rancho Bernardo area of San Diego. In Santa Barbara County, a 600-acre blaze near the city of Lompoc was 50 percent contained.

A wildfire climbs a canyon toward homes Wednesday, May 14, 2014, in Carlsbad, Calif.
A wildfire climbs a canyon toward homes Wednesday, May 14, 2014, in Carlsbad, Calif. (AP)

State fire officials say triple digit temperatures and dry conditions from the drought were making for an unusually busy firefighting season.

Marine Corps officials said military fire crews on Wednesday were fighting a blaze that started at about 9:45 a.m. at the Naval Weapons Station in Fallbrook, north of San Diego, and had spread to more than 100 acres. Residents in military housing have been ordered to evacuate. Students at Mary Fay Pendleton Elementary School, located on base, were also ordered to go home.

Flames from a burning big rig on Interstate 5 on the northern Camp Pendleton coast have spread to about 3 acres of brush. The California Highway Patrol says at least one lane in each direction remains open, but traffic is backing up. It's unclear why the truck caught fire.

Further south, blazes threatened homes in Carlsbad, and prompted the evacuation of Carrillo Elementary School in the neighboring community of San Marcos.

Evacuation orders were lifted for all of the more than 20,000 residents in and around San Diego on Tuesday night just a few hours after they were called, and all but a handful of those in 1,200 homes and businesses told to evacuate in Santa Barbara County had been allowed to return.

The 2.47-square mile blaze was 25 percent contained. It was hoped that number would increase to 50 percent by day's end, San Diego Fire-Rescue spokesman Lee Swanson said.

The Santa Barbara County blaze, 250 miles to the northwest, was 50 percent contained Wednesday morning. Firefighters also adjusted its size downward to 600 acres.

Two firefighters suffered minor injuries -- one heat-related and one from smoke inhalation, Calfire Battalion Chief Ray Cheney said. Neither blaze caused any home damage, but another hot, dry and gusty day was expected as California baked in a spring heat wave as high pressure sat over the West.

In the mountains of southwestern New Mexico, crews battling a 9-square mile wildfire are preparing for high winds this week. And in the Texas Panhandle, about 2,100 residents have started returning to their homes after wildfire burned at least 156 structures. The fire in the Fritch area was 85 percent contained Wednesday.

In San Diego County, record-high temperatures were forecast as were winds of 25 mph with gusts up to 50 mph, which could complicate efforts.

"It's starting to pick up already," Swanson said of the winds. "But our objective is to get to 50 percent containment or more by this evening."

Poway Unified School District reopened schools Wednesday a day after flames erupted in the fire-prone Rancho Bernardo area of the city, driven by hot, dry Santa Ana winds and forced students to be evacuated from schools.

A firefighter puts water on a house fence  May 14, 2014, in Carlsbad, Calif.
A firefighter puts water on a house fence May 14, 2014, in Carlsbad, Calif. (AP)

By late afternoon, the flames ripped through canyons to approach expensive homes and new subdivisions on the ridges. It spread to Rancho Santa Fe, one of the nation's wealthiest communities, known for its multimillion-dollar homes, golfing and horseback riding.

"There's a lot of work to be done today still," Rancho Santa Fe Fire Chief Tony Michel told reporters Wednesday morning. "There are a lot of hotspots throughout the whole area of the fire. Crews will be working diligently to put those fires out. The winds are going to be a problem."

After the fire ignited, the city of San Diego issued between 16,000 and 17,000 evacuation orders, according to San Diego County Sheriff Bill Gore. The Sheriff's Department issued an additional 5,000 evacuation orders outside city limits, Gore said. All the evacuations were called off by around 9 p.m. Tuesday.

Meanwhile, in the Santa Barbara County community of Lompoc, heavy brush and downed power lines provided special challenges for firefighters, said David Sadecki of the county Fire Department.

Some 689 firefighters remained on scene overnight building lines around the blaze.

"We hope the containment lines hold today," Sadecki said.