This post has been updated. See below for details.
Three eastbound lanes of the 60 Freeway in South El Monte were shut down after a motorcyclist was struck and killed by a big rig that fled the scene, authorities said Wednesday night.
The California Highway Patrol issued a SigAlert after the incident, which occurred about 6:45 p.m. near Peck Road and said that the lanes would be closed for an "unknown duration."
Eastbound traffic on the busy artery was backed up for several miles.
Initial reports from officers on the scene indicated that motorcyclist fell and then was hit by the big rig, the CHP said.
Investigators were gathering evidence on the freeway and no additional details were immediately available.
[Updated, 10:35 p.m., Sept. 11: All lanes have been reopened, the CHP said.]