Millions of Southern Californians faced new wildfire warnings on Tuesday, and tens of thousands saw their power shut off as strong winds blew across the parched landscape around Los Angeles where two massive blazes have been burning for a week.

Santa Ana winds that began gusting over the mountains before sunrise were forecast to continue until Wednesday morning with enough force to carry fire-sparking embers for miles and stoke new outbreaks in a region where at least 25 people have already been killed.

“Life threatening and destructive and widespread winds are already here,” LA city fire chief Kristin Crowley told a news conference.

Much of Southern California was under elevated fire risk, with crews on high alert from the Mexican border to Central California, far north of Los Angeles.

Nearly 90,000 households lost electricity as utilities shut off power to prevent their lines from sparking new blazes.

Weary and anxious residents were told to be ready to flee at a moment’s notice.

Police announced roughly 50 arrests, for looting, flying drones in fire zones, violating curfew and other crimes.

The biggest worry remained the threat from intense winds predicted to reach nearly hurricane force in some areas. Tuesday's forecast included a rare warning: The winds, combined with severely dry conditions, have created a “Particularly Dangerous Situation,” the National Weather service said, meaning that any new fire could explode in size.

Gusts were forecast to pick up strength in the evening and into Wednesday before decreasing, and red-flag warnings from Central California to the Mexican border were to remain through most of Wednesday, weather service meteorologist Ariel Cohen said.

Planes doused homes and hillsides with bright pink fire-retardant chemicals while crews and fire engines deployed to particularly vulnerable spots with dry brush.

Los Angeles Mayor Karen Bass and other officials - who were criticised over their initial response - expressed confidence that the region was ready to face the new threat.

With almost no rain in more than eight months, the brush-filled region has had more than a dozen wildfires this year, mostly in the greater Los Angeles area.

Just under 90,000 people in the county remained under evacuation orders, half the number from last week. (AP)