Witnesses said they heard an aircraft engine revving and then a splash in the water, KSBW-TV reported. People on shore later reported seeing debris wash up from the crashed plane.
The twin-engine Beech 95-B55 Baron with three people aboard took off from the San Carlos airport at 10:11 p.m. and was last seen at 10:37 p.m. near Monterey, according to flight tracking data from FlightAware.com.
Searchers in a boat found one person around 3 a.m. Divers found the remaining two people inside the aircraft between 6:30 a.m. and 9:15 a.m. All three were unresponsive, the Coast Guard said.
The Federal Aviation Administration and the National Transportation Safety Board will investigate.