Voluntary evacuation orders were issued as firefighters battled an estimated 850-acre brush fire in Big Bear Monday afternoon.

The blaze was first reported as a 10-acre fire that was "growing rapidly" at Holcomb Valley Road and N Shore Drive in the San Bernardino National Forest.

Evacuations in Holcomb were voluntary, Big Bear Fire Department officials said.

San Bernardin County sheriff's officials said areas also under evacuation were the dump and Baldwin Lake.

Doble Trail and Tanglewood Group campgrounds were both closed.

No structures were threatened. The Pacific Crest Trail was closed west of Highway 18, as well as Van Dunsen Road and Holcomb Valley Road East at Highway 18. Portions of the highway were also shut down.

Fire crews received assistance from seven air tankers and six helicopters, according to officials with the San Bernardino National Forest.

The cause of the fire was unknown.

Temperatures in the area reached 85 degrees as a heat wave continues to sear the Southland. The humidity in the area was low at 10 percent, according to fire officials.

This fire comes as firefighters in Castaic continue to work to contain a 1,000-acre blaze in a remote area amid hot conditions.