Photo: The Canadian Press

Mud and debris that flowed onto Pacific Cost Highway has closed the right lane in an area burned by the Woolsey Fire in Malibu, Calif., Thursday, Dec. 6, 2018.

Authorities kept a worried eye Friday on fire-scarred Southern California hillsides after a storm brought flooding fears and prompted evacuation orders for hundreds of homes.

The second storm in a week dropped record-breaking rains on downtown Los Angeles, jammed major roads and sent an airliner skidding off a runway, but no major injuries were reported.

Mandatory evacuations were ordered for areas of Orange and Riverside counties ravaged by a summer wildfire. Black, surging torrents choked with downed trees and mud swept down channels near homes and in one case swept across a bridge and took out a guardrail.

Other areas saw foot-deep mud or water.

No homes were seriously damaged but even though the storm eased by nightfall, evacuation orders for hundreds of homes in Trabuco Canyon in the Santa Ana Mountains south of Los Angeles and for a few neighbourhoods in the Lake Elsinore area east of Los Angeles remained in place overnight.

Other Lake Elsinore areas had their mandatory evacuation orders downgraded to voluntary evacuation warnings late Thursday night, although fire officials said there was still a potential for dangerous conditions and urged residents to remain vigilant.

Also in Lake Elsinore, firefighters worked into the night lining a street with sandbags to protect homes.

"We just don't know the stability of our hills anymore," Lake Elsinore Mayor Natasha Johnson told KABC-TV earlier. "The fire did its devastation ... the hills behind us that are not a concern could become a concern very quickly."

A mudslide shut down Pacific Coast Highway and surrounding roads in and around Malibu neighbourhoods charred by another fire last month last month that destroyed hundreds of homes.

The end of the storm will be followed by a ridge of high pressure that will bring dry and warm conditions to the area through the weekend but another storm system could move in early next week, the weather service reported.