There was no sign of survivors after hours of searching, ABC News wrote.
The collision occurred about 15:30 on Friday on a dazzlingly sunny day, the Coast Guard said, with no immediate word on what might have caused it.
Two men ages 61 and 81 were aboard one plane, and a 72-year-old woman was aboard the other plane, Coast Guard Capt. Jennifer Williams said.
Searchers found wreckage, including a pilot's logbook, from the Beechcraft plane that was carrying the two men.
The plane flown by the woman is missing, and air traffic controllers saw two aircraft apparently run into each other on radar, leading authorities to conclude they must have collided.
Both planes had taken off from the nearby Torrance Airport, and both pilots were experienced, Williams said.
