Around 3:30 a.m., a man walked onto southbound Highway 680 near the Stoneridge Road exit and was struck by at least two cars and killed, CHP Officer Steve Creel said.
A short time later, the CHP shut down all lanes of southbound Highway 680 from the interstate Highway 580 exit and Stoneridge Road, blocking traffic.
Creel said the drivers involved in the collision are cooperating with the CHP investigation.
"Right now the investigation is focusing on the identity of the pedestrian and how that pedestrian got out on the freeway at 3:30 in the morning," Creel said.
He said the coroner's office arrived at the scene of the crash around 5:30 a.m. to remove the victim's body from the roadway.
The injuries the man suffered in the crash have made it difficult to identify him, Creel said.