A small brush fire in the Diamond Bar area was threatening homes and shut down lanes of the 60 Freeway late Monday morning.
The blaze was reported about 11:35 a.m. when a semi truck somehow caught fire along the westbound 60 Freeway near Phillips Ranch Road, according to the California Highway Patrol.
The fire spread to the hillside and was creeping uphill near homes in the area.
The CHP issued a SigAlert, closing the number 3 and 4 lanes of the highway for about an hour.
The fire had grown to about a quarter acre as of about 12:45 p.m.
Aerial video from Sky 5 showed a charred hillside and flames near homes in the vicinity.
Los Angeles County firefighters on the ground and water-dropping helicopters helped prevent the fire from spreading further.
Firefighters were also providing structure protection on the homes.
The closure caused a miles-long backup on the freeway, aerial video showed.
Forward progress of the blaze had stopped by 1:20 p.m. and no injuries were reported.