DPA/Reuters

Los Angeles/San Diego

More than 1,000 firefighters battled a series of fast-moving southern California wildfires on Thursday that spread across the region despite the efforts of more than 20 firefighting aircraft.

The worst damage was inflicted on the affluent community of Carlsbad, where an out-of-control blaze burnt some 25 homes including an 18-home apartment block.

Another blaze in Camp Pendleton, a sprawling Marine base, forced the evacuation of the San Onofre nuclear power plant.

San Diego County Supervisor Bill Horn told CNN that the timing and location of six of the fires indicated the likelihood of arson.

“The fires were started in six different spots close to roadways,” Horn said. “Six fires like that is too much of a coincidence.”

Late on Thursday, Escondido police said they had arrested two teens on suspicion of arson after locating the pair near a shopping mall.

The two matched descriptions by witnesses of two people trying to set fires in the South Escondido area, police said.

Authorities elsewhere were also investigating how so many fires started about the same time and whether any were intentionally set.

“We all have suspicions, like the public does, when you have nine fires that started all over the county,” San Diego County Sheriff Bill Gore said.

The news channel reported that more than 100,000 people had been ordered to evacuate.

California Governor Jerry Brown has declared a state of emergency in San Diego County to allocate more firefighting resources to the suppression effort.

News clips and videos posted online by residents showed homes on fire in the inland city of San Marcos, with helicopters flying overhead trying to douse the flames with water.

According to Cal Fire (the California Department of Forestry and Fire Protection), the state firefighting authority, the wind-whipped blazes have burnt more than 4,000 hectares since igniting on Wednesday in record-high spring temperatures.

Huge clouds of black smoke hung over much of San Diego County, where the worst blazes were burning on Thursday, driven by the blistering Santa Ana winds, which bring strong, dry gusts out from the interior desert.

The Los Angeles Times reported that non-essential employees were evacuated from the nuclear facility south of Los Angeles due to the fired at Camp Pendleton.

The plant has been offline since 2012, and there was no safety threat to the power station, officials said.

The wildfires broke out during a four-day heatwave.

“In San Diego County, what we’re experiencing over the last several days is high temperatures, low humidity and very high winds. That’s a weather pattern that we usually see in the fall,” Cal Fire spokesman Daniel Berlant said at a press conference. “All it took was the spark of a fire.”

The pace of wildfires recorded by Cal Fire is more than double the average for the first five months of the year, he said.

The fires coincided with a heat wave that has seen record temperatures throughout the normally temperate region for this time of year. The latest drought statistics showed the entire state under extreme drought conditions for the first time since such were logged.

There was good news from weather forecasters, who predicted that temperatures would drop dramatically starting today.

“Unfortunately, Mother Nature was not on our side today,” San Marcos fire Captain Mike Mohler said. “We are cautiously optimistic about the future.”

Meanwhile, several thousand suburban San Diego residents forced to flee a wildfire threatening their towns were allowed to return home early yesterday.

By morning, fire crews managed to establish containment lines around 10% of the fiercest of the blazes, the so-called Cocos fire.

A US Forest Service spokeswoman speaking for the region’s fire command said crews had gained “a pretty good handle” on eight other blazes around San Diego County that had forced as many as 125,000 people from their homes during the week.

Evacuation orders were lifted early yesterday for some 4,600 people living in two San Marcos-area neighbourhoods but remained in effect for the bulk of homes threatened by the Cocos fire, county emergency management and fire officials said.

At least one large home was burned to the ground in suburban San Marcos by the Cocos fire, and television images showed towering flames closing in on other homes as residents scrambled to collect belongings and evacuate.

In all, eight houses and an 18-unit apartment building were known to have been lost this week in various fires across San Diego County, authorities said.

One of the most damaging of those, the Bernardo fire in the coastal city of Carlsbad, was 90% contained by yesterday morning, a day after evacuation orders for the town were lifted.

Crews checking hot spots found a badly burned body in a transient encampment there but officials could not immediately confirm the person was killed by the fire.

Elsewhere, three separate fires that broke out on the sprawling Camp Pendleton Marine Base north of San Diego had charred more than 14,000 acres