All northbound lanes of the 5 Freeway north of Burbank were closed Wednesday afternoon after flooding sent mud and debris across the interstate.
Flooding also closed all but southbound one lane, backing up traffic into Sun Valley.
The California Highway Patrol closed the northbound lanes about 2:30 p.m. as authorities diverted traffic at Glenoaks Boulevard.
Several southbound lanes were also closed at Roscoe Boulevard, according to the CHP, which requested bulldozers and other equipment from Caltrans to clear the roadway.
Aerial television news footage showed flooding, rocks, mud and debris across several lanes. Several vehicles were also stalled in the water, the CHP said.
There was no immediate estimate when the lanes would reopen.
The debris flow comes as the season's first main storm system blows across the region, bringing scattered showers. The storm is expected to move out starting Thursday.