CHP arrived at Highway 4 around 3:30 a.m. in response to reports of a man running through lanes on both sides of the highway east of Harbor Street, CHP Officer Tom Maguire said.
Private security guards traveling through the area had first attempted to restrain him with handcuffs before police arrived, but the man began to fight him, Maguire said.
When CHP officers arrived, the suspect was allegedly continuing to fight, even after CHP put him in leg restraints to subdue him and safely remove him from the center of the highway.
During the struggle, the suspect's body went limp and he stopped breathing, Maguire said. CPR was initiated, and paramedics from the Contra Costa County Fire Protection District were called.
Efforts to resuscitate the man were not successful, Maguire said, and he was pronounced dead. Details regarding the man's identity were not released.
The Contra Costa County District Attorney's Office is continuing an investigation alongside the highway this morning, Maguire said. One westbound lane is closed indefinitely to accommodate the operation.