Los Angeles County firefighters are battling a brush fire near Pyramid Lake that ignited when a big rig erupted in flames along the 5 Freeway on Friday afternoon.

The Emigrant Fire, which is named after a boating facility at Pyramid Lake, erupted near the interstate at Vista del Lago Road just after 1:30 p.m. and quickly grew to 100 acres in the steep and rugged terrain, authorities said.

The flames were reported to be rapidly spreading in a northern direction, away from a twisty stretch of the freeway.

As of 4:20 p.m., the blaze had consumed 220 acres of dry hillside brush and was 5% contained, although firefighters appeared to be steadily gaining the upper hand over it.

“Crews have excellent progress on the fire through an aggressive aerial attack featuring 10 aircraft,” an Angeles National Forest tweet stated.

Firefighting personnel are using the water-dropping helicopters to attack the flames by air, and crews also responded on the ground.

The blaze has the potential to burn about 400 acres, according to the L.A. County Fire Department.

The flames were sparked by a big rig fire that — according to the California Highway Patrol’s incident log — was reported around 1:30 p.m. on the northbound 5 at the Vista del Lago off-ramp and spread to some nearby brush. A SigAlert has been issued in the area and two northbound lanes have been shut down for an unknown duration.

It was not immediately clear what caused the vehicle to catch fire.

No structures were immediately threatened, according to authorities.

The blaze is burning to the north of the Route Fire, which charred more than 400 acres after igniting last Saturday near the 5 Freeway and Templin Highway in the Castaic area.