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A brush fire burning in Topanga Canyon above PCH was 10 percent contained by Thursday night, authorities said.

Smoke rises from a brush fire in Malibu on June 29, 2017. (Credit: KTLA)

The two-alarm fire was reported at Topanga Canyon Boulevard and Pacific Coast Highway, Los Angeles County Fire Department Inspector Gustavo Medina said about 3:30 p.m.

By 4:30 p.m., fire officials were estimating 20 to 25 acres had burned in the unincorporated Topanga area. Crews did not report an increase in that figure as the night wore on.

Earlier in the evening flames were moving uphill in medium-to-heavy brush and structures were threatened, Medina said.

Although firefighters told residents they should be prepared to leave their homes, evacuations remained voluntary on Thursday, according to LACFD Inspector Richard Licon.

“Our crews are making good progress. It’s just the steep terrain,” he told KTLA. “We’re getting those boots on the ground to get a good containment line around it.”

Aerial video showed smoke and large flames rising from a rugged, heavily vegetated area well up the canyon. Water-dropping helicopters were responding.

A helicopter drops water on a brush fire in Malibu on June 29, 2017. (Credit: KTLA)

The address reported by the Fire Department is near Topanga State Beach and the popular Reel Inn seafood restaurant. The Getty Villa museum is not far away. The Los Angeles Fire Department, which was responding alongside county firefighters, said the fire was reported at 3:20 p.m. at 4000 S. Topanga Canyon Blvd.

LAFD’s Brian Humphrey said flames were moving slowly and were driven by terrain.

Topanga Canyon Boulevard was closed, he said. Drivers were advised to expect severe delays.

A brush fire was also burning in Calabasas on Thursday afternoon.

The Southern California region has been hit with multiple  brush fires over the past couple of weeks.

When a 10-acre fire burned near homes in Burbank Wednesday afternoon, a battalion chief there said the wet winter had allowed copious brush to grow over spring. That vegetation is drying out and providing fuel for fires, he said.