The crash was reported shortly after 9 a.m. on the Buchanan Street off-ramp, CHP Officer John Short said.
A big-rig apparently struck a vehicle on the off-ramp and then drove off, Short said.
Short said someone in the vehicle that was hit died, and the Alameda County coroner's office has been called to the scene, Short said.
The big-rig, which has a rusty trailer, had not been found as of 9:30 a.m., he said.
The off-ramp remained closed as of 9:40 a.m.
