The fire was burning west of San Gabriel Canyon Road (State Route 39) and uphill away from structures. As of 11 p.m., the fire charred about 190 acres and was 5 percent contained.
There was no immediate threat to residences. Structure protection was underway just in case. Azusa police said evacuations were ordered for Foxtail Court.
Street closures in the Duarte area have been ordered due to the fire burning north of Fish Canyon. Huntington Drive is closed at Encanto Parkway. All residential streets that intersect with Encanto Parkway north of Huntington Drive into Fish Canyon have also been closed.
Encanto Park has been closed and is being used as a staging area for water dropping helicopters.
Two "super-scooper" fixed-wing water-dropping aircraft and about 150 firefighters were on scene. No injuries were reported.
The cause of the fire, dubbed the "Madre" incident, was under investigation.