Cars are swept away by mudslides on Ocean View Boulevard after an intense storm brought down hillsides in wildfire burn areas north of Los Angeles on Saturday. (Mike Meadows/Associated Press)

Mudslides swept away cars and pushed furniture out of homes and into the streets in the foothills north of Los Angeles on Saturday as an intense storm brought down hillsides in wildfire burn areas.

At least 41 homes were seriously damaged and 500 more were ordered evacuated after heavy rains overflowed debris basins, carried away cement barricades and swept cars into storm drains.

"We've got crews going door to door to tell residents to get out," said Los Angeles County Fire Insp. Frederick Stowers. "Some of the roads up there are a complete mess."

At least 30 centimetres of debris was reported in some houses. Family photographs, furniture and other personal items were spotted among the rocks and debris that flowed into yards and streets.

Evacuations were ordered in foothill areas of La Canada Flintridge, La Crescenta and some parts of Acton.

An evacuation centre was set up at La Canada High School and the Red Cross was working to establish other locations to shelter displaced residents.

Crews used bulldozers and other heavy equipment to clear masses of mud and rocks that blocked suburban streets and intersections.

At least 30 of the damaged homes were on Ocean View Boulevard in Pickens Canyon.

Five homes were tagged with a red notice warning they were unsafe to enter. At one house, mud was piled up to the handle on the front door and the yard was washed away, replaced with muck, rocks and a tangle of tree roots. Two white Toyotas were smashed against the front of the house.

At another nearby red-tagged home, crews dug by hand through more than a metre of mud to try to find the source of a natural gas leak. Workers in the area said at least one house had shifted off its foundation.

No injuries were reported as a result of the mudslides.

Widespread flooding and downed trees tied up traffic and caused accidents across Los Angeles County. A section of the Long Beach Freeway was shut down early Saturday because of high water.

Water almost 30 centimetres deep flowed into businesses on Melrose Avenue. To the east, Topanga Canyon Boulevard was closed by a rockslide just north of the Pacific Coast Highway, and scattered rocks and mud fell on roads in Malibu.

Scattered power outages affected more than 10,000 customers in the Los Angeles area.