A blaze in rural hills of Ventura County northwest of Los Angeles spread over 6,000 acres more than nine square miles threatening the northwestern area of the city of Moorpark, said county fire spokesman Bill Nash.
Evacuations were ordered for scattered ranches and homes. Fire Capt. Ron Oatman couldn't provide a specific number but said numerous homes and electrical infrastructure were threatened. One small building was seen ablaze.
"Don't wait for an evacuation order if you feel like you're in danger," he said.
Air tankers including a DC-10 jumbo jet and big helitankers bombarded the flames with retardant and water while hundreds of firefighters worked on the ground. Two minor injuries to firefighters were reported.
Temperatures topped 100 and humidity fell to single digits while winds gusted to 30 mph, Nash said.
"Those are all the ingredients you need to make a fast-moving fire," he said.
City spokesman Hugh Riley said the water district authorized avocado growers to turn on irrigation sprinklers in their orchards. He noted that the fire was following the path of a blaze several years ago.
"That was a big one and fortunately it burned a lot of the fuel that could feed this one," he said.
Another fire broke out in Riverside County, 40 miles east of Los Angeles, and burned from the city of Riverside into the city of Norco and toward adjacent Corona. Norco Fire Chief Jack Frye said the 120- to 150-acre fire was up to 60 percent contained and no homes had been lost despite gusts up to 45 mph.
In neighboring San Bernardino County, a 17-acre blaze damaged unidentified structures in Redlands. City spokesman Carl Baker said a dozen homes were evacuated. Containment was estimated at 50 percent.
The fires were whipped by the region's notorious Santa Ana winds, which blow from the northeast, speeding up and warming as they descend through mountain passes and canyons and push seaward. The air is extremely dry, lowering humidity levels and making brush easier to burn.
The Santa Anas also whipped up clouds of ash north and east of Los Angeles in the vast area of the San Gabriel Mountains burned over by a gigantic wildfire that continues to smolder a month after it began.
The winds caused some increased fire activity on ridgetops in the San Gabriels, but the haze was from blowing ash, not smoke columns, said Carol Underhills, a public information officer for the U.S. Forest Service.
The fire burned across 160,557 acres - 251 square miles - of Angeles National Forest after it was ignited by arson on Aug. 26. At its peak it destroyed 89 homes and caused two firefighter deaths.
The fire remained 94 percent surrounded Tuesday, and fire commanders again pushed back the projected date for full containment, this time from Tuesday evening to Thursday morning, due to the weather.
About 600 firefighters watched for flare-ups.
"One of your main concerns is the fire that's down but not out coming back at ya," said Forest Service spokesman Robert Brady.
The weather service also issued "red flag" warnings of fire weather conditions in other parts of California due to a combination of low humidity, high temperatures and wind.
Those areas included the hills east of San Francisco Bay and mountains to the north, the northern Sierra and northern Sacramento Valley and a large swath of the state farther north.