The Portola Fire was first reported around 2 p.m. in the 9800 block of West Portola Drive and was said to be threatening homes in multiple neighborhoods.
Firefighters were working to contain the blaze to the area east of Benedict Canyon, south of Yoakum Drive, west of San Ysidro Drive and north of Portola Drive.
The Los Angeles Fire Department said the cause of the fire was determined to be a contractor using a weed wacker to clear brush in the 9800 block of Portola.
About 86 homes in various neighborhoods had been ordered evacuated, but the evacuations were lifted by 8 p.m., officials said.
Evacuations were ordered on San Ysidro Drive between Milboro Place and Beeson Drive, including on Beeson and Milboro themselves.
Additional evacuations were ordered along the northern boundary of Highridge Drive down Summitridge Drive and continuing on San Ysidro Drive to Stan Place to the south.
With only light winds, firefighters reported making good progress against the blaze.
An evacuation shelter was established at the Westwood Recreation Center at 1350 S. Sepulveda Blvd.
Police were also ordering several street closures, including Benedict Canyon northbound at Tower Road; and San Ysidro at Pickfair. Local residents will be allowed in with proper identification.
Firefighters were mobilizing multiple engine companies to put structure defense in place.
More than 250 firefighters were assigned to the blaze, which had burned through 35-40 acres by the afternoon, with an estimated 40 percent containment by 10 p.m. Fire crews were using five helicopters to make water drops and four fixed-wing aircraft to drop flame retardant along the ridgelines.
Two firefighters suffered minor injuries fighting blaze, one with heat exhaustion and one with a minor burn.
Firefighters said it had the potential to grow to 60 acres. But they also said the spread of the blaze was relatively slow amid 9 mph winds, though the rugged, steep terrain provided additional challenges to firefighters.
"Firefighters are working hard and fast and they're making progress," said Los Angeles Fire Department Capt. Erik Scott.
Officials also advised residents in other nearby neighborhoods to consider evacuating, including in the areas of Benedict Canyon Drive from Portola to Yoakum drives, as well as at the northern boundary of San Circle down San Ysidro Drive to the southern boundary of Peavine Drive.
"Better to leave early than late and allow us access so we can defend the structures," said Margaret Stewart, spokesperson for the LAFD.
People who have pets are being advised to take them along when they evacuate. The city was providing temporary shelter for pets of evacuees at the East Valley shelter, 14409 Vanowen St., Van Nuys.
For those who are evacuating due to #PortolaFire, please take your animals with you. If you need temporary shelter for your cats, dogs & other small pets, please visit the East Valley Animal Services Center at 14409 Vanowen Street, Van Nuys, CA 91405 for assistance.— LA Animal Services (@lacitypets) June 12, 2018
The fire was burning in heavy brush that had not been burned for years. Firefighters were facing additional challenges because of the hillside neighborhood's narrow streets and limited access points.