Dozens of firefighters have been dispatched to battle a blaze burning in the hills above Azusa that prompted the closure of Highway 39 on Thursday afternoon.
The Dam Fire erupted in the 9500 block of North San Gabriel Canyon Road, near Morris Dam in the Angeles National Forest, the Los Angeles County Fire Department tweeted shortly before 1:45 p.m.
The fire rapidly grew to 120 acres within an hour of it first being reported, according a tweet from the Angeles National Forest. Flames are spreading uphill in heavy brush.
Along with 100 firefighters, two water-dropping helicopters have been sent to mount an aerial attack on the blaze.
Plumes of heavy smoke were visible from nearby homes, photos showed. But no structures were immediately threatened, according to officials, and evacuations have not been ordered.
Highway 39 has been indefinitely shut down in both directions.
Check back for updates on this developing story.