The burned hillsides in the Angeles National Forest run to the edge of Tujunga, Calif. (Chris Carlson/Associated Press)

Fire crews battling the massive wildfire north of Los Angeles are shifting their efforts away from the western front in an effort to keep the flames from spreading into eastern suburban communities.

The Station fire, which has burned more than 585 square kilometres of the Angeles National Forest, is pushing east toward Monrovia, Sierra Madre and Pasadena, and efforts to fight the flames were being shifted to those areas, officials said.

About 5,000 homes in the region were classified as threatened on Friday.

Most of the western flank of the 11-day-old fire, which is in rugged canyons, has been contained through the work of hand crews and water drops by helicopters, said U.S Forest Service Cmdr. Mike Dietrich.

But even areas where the flames have been tamed are still filled with smoke and smouldering remains, officials said.

The fire is now about 42 per cent contained, officials said. Full containment of the blaze isn't expected until Sept. 15.

Crews have credited lower temperatures with allowing them to make gains in battling the fire.

United States Forest Service firefighters grab a late-night meal at Hansen Dam Recreation Center in Lake View Terrace, Calif. (Jason Redmond/Associated Press) At the wildfires' peak, thousands of residents living in the Los Angeles foothills were forced to evacuate and 12,000 buildings were threatened. At least 64 homes were destroyed and at least three people injured.

Officials announced on Thursday that forensic evidence suggests the fire, one of the largest in Southern California's history, was started by arson. Officials have not disclosed what the evidence is.

The conclusion has prompted a homicide investigation because two firefighters died on Sunday night when their truck plunged off of a steep mountain road shrouded in thick smoke.

Meanwhile, an eight hectare wildfire broke out Friday in the Cleveland National Forest in Orange County, about 100 kilometres southeast of the Station blaze.

With files from The Associated Press