LOS ANGELES — Firefighters in Southern California braced for another day of hot, extremely dry weather as they battled two wildfires in the Angeles National Forest northeast of Los Angeles, while crews worked to contain another blaze in a rural area of Northern California that consumed a mobile home.

A fast-moving wildfire started Wednesday afternoon about 20 miles southwest of King City in Monterey County and consumed more than 3 square miles of grassy, rolling hills, Division Chief Curt Itson of the state Department of Forestry and Fire Protection said.

The fire was 30 percent contained early Thursday, Itson said, but residents of 20 homes near the tiny community of Lockwood evacuated voluntarily. The cause of the blaze was under investigation.

Northeast of Los Angeles, two wildfires fouled the air for millions of Southern Californians, but the flames were burning away from foothill suburbs and no homes were threatened.

The National Weather Service predicted another hot, dry day Thursday with moderate mph winds out of the west, very low humidity and temperatures as high as 104 degrees at low elevations of the Angeles National Forest.

Stoked by the arrival of high temperatures and extremely dry air after weeks of unusually mild summer weather, the 2.6-square mile Morris Fire in Angeles National Forest produced a pungent white haze that spread through the Los Angeles Basin and east into San Bernardino County. The smoke lingered for lack of a sea breeze.

"It's pretty bad, the smoke," said Natacha Cuvelier, a 20-year-old student at the University of Southern California in Los Angeles. "Once I stepped out of the door, I could smell it."

The air was considered unhealthy in many areas, and regional officials urged people to avoid strenuous activities, indoor and out.

Schools were advised to suspend physical education and sports, said Dr. Jonathan Fielding, Los Angeles County's director of public health.

"Sometimes when we have these fires that will last for several days, the smoke can kind of build and get sloshed back and forth, so to speak," said Sam Atwood, spokesman for the South Coast Air Quality Management District. "With each successive day, the extent of the smoke will get bigger and bigger."

Late Wednesday, a new fire erupted in the Los Angeles suburb of La Canada Flintridge. At least 20 acres had burned by evening with 20 percent containment, U.S. Forest Service spokesman Bruce Quintelier said.

The weather service has issued a fire danger warning for mountain areas stretching from Los Angeles County northwest through Santa Barbara and Ventura counties, but the forecast did not call for any strong Santa Ana winds that typically stoke the worst Southern California wildfires.