Officers found the man suffering from a gunshot wound in a trailer parked in the backyard of a home near Princeton Street and Sunset Boulevard, Alameda County Sheriff's Sgt. J.D. Nelson said.
Police received had reports of multiple gunshots fired in the area a short time after midnight, he said.
The victim, who appeared to be in his late 20s, was rushed to a local hospital, where he died from his injuries.
No other injuries were reported in the shooting.
Nelson said the sheriff's office has not identified a suspect. Investigators are questioning possible witnesses in the area this morning as part of the homicide investigation, he said.
Sheriff's and coroner's personnel are working to identify the victim.