Parts of Burbank, Glendale and Sunland-Tujunga were under evacuation orders for the La Tuna Fire.
The Burbank evacuations were lifted by 10 p.m. Saturday, but the others remained in place.
Officials believe the La Tuna Fire is the largest blaze by acreage in Los Angeles city history.
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At one point the fire was estimated at 8,000 acres, but later Saturday night fire officials issued a revised estimate of 5,800 acres.
The La Tuna Fire has burned three structures and was 10 percent contained Saturday night, according to the Los Angeles Fire Department.
About 800 firefighters from multiple agencies were fighting the flames Saturday night and the battle was expected to go strong through the evening and well into Sunday.
Temperatures remained warm at night, with an overnight low of only 80 degrees expected.
Southeast winds of 5-10 mph were also fanning the flames, and sending embers to create new spot fires, said LAFD Capt. Erik Scott.
He said the winds had shifted several times during the day, making the fire spread in multiple directions and increasing the challenges for firefighters.
"We've increased the number of firefighters on scene," Scott said in a Saturday night briefing. "We have a very active fire that is spreading in multiple directions. However, we do feel we do have the appropriate quantity and type of resources on scene."
Two firefighters were treated for dehydration, but no other serious injuries were reported to firefighters or civilians.
A helicopter also apparently went through some mechanical difficulties and made a precautionary landing at Verdugo Hills High School. No injuries were reported.
Los Angeles Mayor Eric Garcetti signed a declaration of emergency for the fire Saturday, calling on all the city's available resources to protect residents.
"The La Tuna Canyon Fire is an emergency that requires all available resources to protect our residents and keep our homes and other structures out of harm's way," Garcetti said. "We are grateful for the men and women of LAFD and all our partner agencies, for their heroic efforts to attempt to bring the fire under control and to keep people and their homes safe."
The declaration calls on all city departments to take all necessary steps to protect life and property in the area affected by the fire.
It also asks Gov. Jerry Brown to declare an emergency, to help speed up assistance from the state and federal governments.
The U.S. Federal Emergency Management Agency has already authorized the use of federal funds to help firefighting efforts.
FEMA provides Fire Management Assistance Grants which can fund up to 75 percent of eligible firefighting costs. Expenses covered by the grants can include expenses for equipment, materials, supplies and mobilization and demobilization efforts related to fighting the fire.
The windswept blaze was burning in heavy hillside brush in the Sun Valley and Sunland-Tujunga areas, and then moved over the hills toward Burbank late Friday night.
Firefighters moved into structure defense mode to protect homes as residents were advised to evacuate immediately.
A smoke advisory was issued by the Los Angeles County Department of Public Health for the San Gabriel Valley to the San Fernando Valley and Glendale as plumes billowed into the air. Residents were urged to limit outdoor activities.
Firefighters initially feared the flames would reach homes by midnight Friday. But the structure-protection efforts were able to hold off the flames until Saturday morning, when one home was lost near Verdugo Crestline Drive and Alene Drive in Sunland-Tujunga, officials said. Two other structures in that neighborhood were later destroyed.
Firefighters took the unusual step of keeping their water-dropping helicopters in the air at night, outfitting crew members with night-vision goggles. Officials said those goggles were purchased with funds donated to an LAFD foundation.
About 730 homes were evacuated: 300 in Burbank, 250 in Glendale and 180 in Los Angeles, LAFD said.
In other nearby neighborhoods, nervous residents packed up essentials but stayed near their homes and watched the flames with a mix of fascination and dread.
"It's actually really scary because we've never had a fire this close to us," said Tujunga resident Jessica Fernstrom.
WATCH: Mayor, LAFD chief provide update on La Tuna Fire
The blaze was first reported Friday around 1:30 p.m. in Sun Valley. Firefighters initially thought they had a good handle on the blaze. It only burned about a quarter acre of brush as it moved uphill.
"It was actually traveling in a northern direction (and) hopped the freeway, and we were initially worried about the homes on the northern side," said LAFD Capt. Branden Silverman.
"But then we had that storm cell come through. We had a little bit of rain, and that was enough to push the fire in a totally different direction," the captain said. "It started traveling south toward the Burbank city limits."
The fire ignited amid triple-digit heat in the San Fernando Valley. Temperatures were expected to reach a high of 101 degrees in Sun Valley on Saturday, according to the National Weather Service.
The flames and smoke did not immediately affect flights out of Bob Hope Airport in Burbank.
Los Angeles city and county agencies used water-dropping helicopters and Super Scoopers to help fight the flames from the air.
The cause of the fire was unknown.
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