LOS ANGELES — A massive brush fire, called the largest ever in terms of acreage to burn within Los Angeles' city limits, had claimed one home Saturday and was threatening others, authorities said.

Hundreds of firefighters, backed by water-dropping planes and helicopters, were battling the flames in triple-digit temperatures. The fire had blackened 5,000 acres by 10 a.m. PT Saturday and was moving toward Burbank, where much of southern California's entertainment industry is situated.

Evacuations had been ordered in affected neighborhoods.

The fire began Friday afternoon in the steep hills near the Foothill Freeway, commonly called the 210.

The fire spread a pall of thick brown smoke that could be seen throughout greater Los Angeles and dropped ash on many communities during the hot holiday weekend.

Lauding the "heroic job" by firefighters, Los Angeles Mayor Eric Garcetti said it was the largest fire ever in terms of acreage within the city limits. Many others, including some that have been larger and claimed hundreds of homes, have burned through metropolitan Los Angeles County over the years.

There were no reported injuries, though authorities were concerned about reaching homeless people — Garcetti called the "unhoused Angelenos" — living in the canyons.

Firefighters, backed by five engines, were trying to save the single home that had so far been caught by the flames in Sunland-Tijunga area, fire officials said.

The fire was only 10% contained, but was burning slowly due to light winds early in the day.

"The biggest factor is the weather and the wind," Fire Chief Ralph Terrazas told reporters. "We are constantly evaluating the wind."

He said additional water-dropping aircraft had been requested from the state.

Fires also raged across the northern part of the state Saturday, with two dozen active fires reported by the state's Cal Fire agency. Eleven fires were identified as burning in the state's northern counties and into southern Oregon.

Smoke from the wildfires created an expansive layer of haze that blanketed San Francisco and exacerbated the affect of record temperatures set across a costal region typically cooled by fog.

While Mark Twain may have famously opined that the coldest winter he'd ever experienced was a summer in San Francisco, on Friday the city's high of 106 set an all-time record, beating a previous high of 103 in 2000. Bay Area temperatures are expected to drop into the 70s by Labor Day.

Contributing: Marco della Cava in San Francisco