The Norte fire broke out in the coastal city of San Clemente and was driven by wind into neighbouring San Juan Capistrano, the Orange County Fire Authority (OCFA) said. Firefighters worked through the night by land and air to attack the flames and strengthen containment lines.
As of Saturday morning, the fire had spread to 570 acres (230 hectares) and was 5% contained, with wind gusts of 50-70 mph (80-110 km/h) reported.
In a statement posted to social media on Saturday, an OCFA official said six homes had been destroyed or damaged, two firefighters had been injured and the cause remained under investigation. The two firefighters were taken to hospital with heat-related injuries.
OCFA Chief TJ McGovern confirmed at a press conference on Friday that there had been no reports of resident injuries or deaths. "Due to weather and topography, this fire moved fast. This was a wind-driven event," he said.
About 6,000 homes were under mandatory evacuation by Friday night, affecting about 16,000 residents. An evacuation shelter has opened in each of the two cities.
The fire was one of several in the region hit by Santa Ana conditions: dry, warm gusts that blow from the interior toward the coast. The National Weather Service said the winds would linger through Saturday, with the potential for extreme fire behaviour and rapid spread.