All southbound lanes of the 405 Freeway were closed for hours in the Westwood area Monday morning due to a multi-vehicle crash that left one person dead.

Officials said the crash occurred around 3:30 a.m. near Sunset Boulevard and involved four to five cars. One person, a pedestrian, was pronounced dead at the scene.

Sgt. Steve Esquivel of the California Highway Patrol said the presence of the pedestrian is still under investigation.

“We don’t know exactly what led to the pedestrian walking … At some point, they either got out of a vehicle or they were [walking] on the 405 Freeway,” he said.

The CHP issued a SigAlert around 4 a.m., blocking all southbound lanes of travel.

Video from the crash scene showed car parts and debris scattered across the freeway. Traffic backups extended into the Sepulveda Pass.

The HOV, No. 1 and No. 2 lanes were reopened at about 7 a.m., and the No. 3 and No. 4 lanes reopened at about 8:30 a.m., according to the CHP.

During the closure, cars were diverted at Skirball Center Drive.

The cause of the accident was under investigation, and no other injuries were reported.