A fire raging in the San Bernardino National Forest grew another 1,000 acres overnight as it continued to burn through brush and timber in steep terrain.
The Lake Fire in San Bernardino County has forced evacuations and continued Friday to threaten between 150 and 200 structures, some of them historic, according to Lyn Sieliet of the U.S. Forest Service. Officials later upped that figure to about 400.
More than 1,300 firefighters were battling the fire, which started Wednesday. More arrived through the night to prepare for the day's attack, while aircraft provided infrared images and made water drops.
"We're using our aircraft to the maximum capabilities. We're going to depend on the firefighters on the ground to get into the wilderness areas and cut a line to try and stop the fire, and we're just going to try and get out in front of it is the plan for today," Sieliet told KPCC.
Firefighting efforts were being helped Friday by slightly higher humidity, but higher temperatures and stronger winds expected later in day were concerning, Sieliet said.
She said more firefighters were expected to arrive Friday or Saturday.
So far no injuries have been reported and no structures damaged or lost.
Some residences and cabins off of Rainbow Lane and from Angeles Oaks through Lake Williams were in evacuation zones, Sieliet said, though she was unsure how many people were affected because some of the cabins were used for recreation and it was unclear if they were occupied.
Smoke advisories remained in effect for the eastern San Bernardino mountains, portions of eastern Riverside County and the Coachella Valley, with air quality reaching the "Unhealthy" level and potentially higher depending on winds and fire containment, according to the South Coast Air Quality Management District.
Portable monitors detected elevated levels near the city of Desert Hot Springs Friday morning, AQMD spokesman Sam Atwood told KPCC.
Residents in smoke advisory areas should not do any vigorous exercise outside, "especially if they can smell smoke or see smoke, " Atwood said. "If they already have some form of heart or lung disease they should consider staying indoors and try to reduce exposure to any smoke."
Atwood said the National Weather Service's forecast of a possible shift in winds may bring smoke back into the Inland Empire and Los Angeles Basin on Friday night and over the weekend.
This story has been updated.