The planes collided at around 3:30 pm (local time) yesterday and apparently went into the water about two miles outside the harbor entrance, US Coast Guard and other officials said. It was unknown how many people were on board.
Fire and lifeguard boats and rescue divers swarmed the area.
"They found both a partial tail number and then a second tail number," Los Angeles County lifeguard Captain Ken Haskett said.
As darkness fell, about two dozen divers were on call to scour the area but the planes may be at the bottom in up to 30 meters of water, Haskett said.
