A wall of flames dozens of feet high has advanced on a hillside community near San Diego, threatening to destroy upscale houses as eight other major blazes burned in Southern California, keeping thousands of people out of their homes.
US news video showed the rapidly moving bushfire scorching trees and brush as it descended a steep ridge toward a hilly neighbourhood in San Marcos, 48km north of San Diego.
Bright orange flames twisted in the wind, sending thick columns of smoke aloft and blacking out the sky. Fire engines with emergency lights flashing moved along the winding streets of the neighbourhood of large Spanish-style homes.
The destructive cluster of fires comes as California enters its peak fire season in the midst of one of its worst droughts in decades, setting the stage for what state officials worry could be a particularly intense and dangerous year.
It was not immediately clear if the latest advance of the flames had damaged any houses in San Marcos, but officials said the fire had already destroyed three buildings. On Wednesday, it forced the evacuation of one California State University campus.
The nine blazes raging in the San Diego area have destroyed more than 4,047 hectares, forcing evacuation of about 125,000 residents, county officials said.
"It looks like activity has picked back up pretty rapidly," said Cal-Fire spokeswoman Lynne Tolmachoff, who could not immediately provide further details on the San Marcos fire.
Before the advance of flames on San Marcos, firefighters had hoped to take advantage of a lull in windy conditions to try to gain the upper hand against the wildfires.
The blaze in the San Marcos area has ranged across about 324 hectares in steep terrain and is the top threat in the county with containment at only 5 percent, officials said. No major injuries were reported as a result.
"As you stand here today, you can tell it's extremely hot, it's dry, we're in early May, we have a long fire season ahead," Cal-Fire Battalion Chief Nick Schuler told reporters.
Another blaze that broke out on the Camp Pendleton Marine Base north of San Diego had charred 2,430 hectares.
The San Diego Unified School district and other districts canceled classes.
Officials in the coastal city of Carlsbad said a 162-hectare fire in that area was about 60 percent contained and they lifted some evacuation orders. The blaze has destroyed 18 apartment units, four houses and two commercial buildings, the city said on its website.
California Governor Jerry Brown has declared a state of emergency to free up resources to combating the fires.