A wildfire fanned by hurricane-force wind ripped through northwestern Los Angeles foothills on Saturday, forcing some 10,000 people to flee their homes and threatening the power supply of California's largest city, Reuters reported.
A separate fire burnt a second day in the celebrity enclave of Montecito, where 111 homes have been destroyed.
Los Angeles Mayor Antonio Villaraigosa said the fire in the foothills near Sylmar had already destroyed dozens of structures -- more than any other in the past decade -- and that the flames could take down power lines feeding the city.
"The fire is threatening the power of the city of Los Angeles," Villaraigosa told a news conference. "We may have to move to rolling blackouts."
He urged residents to conserve power to avoid outages and to evacuate if they were in the fire's path.
"If you wait until the fire gets there you have waited too long," Villaraigosa said. "This fire can be on you in a moment's notice."
Police closed down Interstate 5, the main freeway linking Los Angeles to the north, and other roads as 600 firefighters mobilized. Transmission lines bringing power follow the I-5 corridor through the mountains north of the city.
Television showed mountains engulfed in flames and billows of smoke as the sun rose on Saturday and Los Angeles County Fire Department spokesman Sam Padilla said the fire was spreading.
High temperatures have dried out the vegetation, making them especially vulnerable, and when the wind picks up, it can carry the flames swiftly across large swathes, Padilla said.
About 2,600 acres (1,050 hectares) were burnt so far and gusts in the area exceed 75 mph (120 kph). A map of the fire is at http://tinyurl.com/sayrefire.
Firefighters, two of whom have suffered minor injuries, are trying to stop the blaze before it reaches Santa Clarita, a bedroom community about 40 miles (64 km) from the centre of Los Angeles with a population of 180,000.
A second fire ravaged hills above Southern California's Santa Barbara coast for a second night after roaring through the exclusive Montecito enclave levelling 111 homes.
Those reported to have lost houses in the community dubbed "America's Riviera" included actor Christopher Lloyd, best known as the zany scientist in the "Back to the Future" movies.
The Montecito fire started on Thursday evening and scorched about 1,800 acres (730 hectares) by Friday morning, devouring mansions and luxury estates tucked into the canyons and foothills of the town 90 miles (145 km) northwest of Los Angeles.
Large swaths of the picturesque community, one of the nation's priciest, were turned into charred, grey landscapes where gates and walls surrounded piles of rubble -- all that remained of multimillion-dollar houses.
The area remains on "red flag" warning for more fires because there is still very little humidity and the gusts could pick up any time, said Daniel Berlant, a spokesman at the California Department of Forestry and Fire Protection.
"It's the dry conditions that make it perfect for more fires," he said.