Updated: Downed Plane Report a 'False Alarm.'

Updated 6 p.m.: All units are off scene.

Updated 5:15 p.m.: Los Angeles County Fire Department Capt. Brian Kane told Patch that reports of the downed aircraft were apparently a "false alarm."

Sheriff's deputies and at least two fire units answered a call of smoke in the hills, and authorities blocked roads around the intersection of Lake Avenue and Loma Alta while they checked out the report.

As of this evening, official found no downed aircraft and could see no smoke.

Updated 5:12 p.m.: Authorities blocked off roads around the intersection of Lake Avenue and Loma Alta, but reported that smoke is no longer visible in the hills above.

Updated: CNS, citing ABC7, reports that a Sheriff's helicopter is searching the foothills of Altadena near the intersection of Lake Avenue and East Loma Alta Drive for a downed aircraft.

Earlier: Altadena Search and Rescue is responding to reports of a possible downed plane in the area around Cobb Estate, authorities said.

An air unit has been dispatched to check out several reports of smoke in the Angeles National Forest above Lake Avenue in Altadena, said Lt. Robert Blume, the watch commander at Crescenta Valley Sheriff's Station.

At this point, the search and rescue dispatch is a precautionary measure, he said. 

Stay tuned! We're heading out to the scene and will post updates when we have them.

Editors Donna Evans and Dan Abendschein contributed to this report.