Wildfires menacing Los Angeles have killed at least 10 people and devoured nearly 10,000 structures, with five fires burning into a third night as dry desert winds fanning the flames again gathered strength.
The Palisades Fire between Santa Monica and Malibu on the city's western flank and the Eaton Fire in the east near Pasadena already rank as the most destructive in Los Angeles history, consuming more than 13,750 hectares and turning entire neighbourhoods to ash.
The death toll from the blazes rose to 10, Los Angeles County's Medical Examiner said in an update late on Thursday, without providing identities or other details.
Los Angeles County Sheriff Robert Luna told an earlier news conference he expected the number to grow.
"It looks like an atomic bomb dropped in these areas. I don't expect good news, and we're not looking forward to those numbers," Luna said.
Private forecaster AccuWeather estimated the damage and economic loss at $US135 billion to $US150 billion ($A218 billion-$A242 billion), portending an arduous recovery and soaring homeowners' insurance costs.
"We're already looking ahead to aggressively rebuild the city of Los Angeles," said Mayor Karen Bass, a Democrat, who faced criticism from President-elect Donald Trump and other Republicans over her handling of the disaster.
President Joe Biden, who declared a major disaster on Tuesday, promised on Thursday that the federal government would reimburse 100 per cent of the recovery for the next 180 days to pay for debris and hazard material removal, temporary shelters and first responder salaries.
"I told the governor, local officials, spare no expense to do what they need to do and contain these fires," Biden said after meeting senior advisers at the White House.
In all, five wildfires burned in Los Angeles County, with the largest Palisades Fire just six per cent contained and the Eaton fire uncontained.
Skies buzzed with aircraft dropping retardant and water on the flaming hills.
A large Super Scooper aircraft on loan from Canada was damaged and grounded after hitting an unauthorised civilian drone near the Palisades fire, the LA County Fire Department said. There were no injuries.
One rapidly growing blaze broke out on Thursday near Calabasas, one of the wealthiest cities in the US and home to numerous celebrities and gated communities.
The so-called Kenneth Fire expanded to 388ha in a matter of hours.
With nerves on edge, Los Angeles County mistakenly sent an evacuation notice countywide to a population of 9.6 million, even though it had been meant only for the area of the Kenneth Fire, officials said. A correction was quickly sent.
At least 20 arrests have been made for looting.
The city of Santa Monica, which is next to Pacific Palisades, declared a curfew because of the lawlessness, officials said.
National Guard troops arrived in Los Angeles on Thursday evening and will help protect property.
Officials said the Eaton Fire had damaged or destroyed 4000 to 5000 structures while the Palisades Fire destroyed or damaged another 5300 structures.
Some Pacific Palisades residents ventured back to areas the fire had already swept through, where brick chimneys were left looming over charred waste and burnt-out vehicles.
Winds dropped on Thursday from the 160k/h gusts seen earlier in the week, permitting crucial aerial support for crews on the ground.
But officials said winds intensified again overnight, and red flag conditions were expected until Friday afternoon.
Firefighting crews managed to fully control the Sunset Fire in the Hollywood Hills, after flames had raged atop the ridge overlooking Hollywood Boulevard's Walk of Fame on Wednesday night.
In Pacific Palisades, once-palatial homes stood in ruins, while downed power lines and abandoned cars littered the roadways.
Aerial video showed block after block of levelled homes, while satellite images showed the two largest fires forming a pincer around the city and thick plumes of smoke from the fires being blown out over the Pacific Ocean.
The homes of movie stars and celebrities were among those consumed by flames.
Actor Jamie Lee Curtis said on Thursday her family would donate $US1 million to relief efforts.
Firefighters from half a dozen other US states and Canada were being rushed to California, in addition to US federal personnel and materiel.
"To our American neighbours: Canada's here to help," said Canadian Prime Minister Justin Trudeau, whose country has experienced its own severe wildfires.
