A 30-year-old man in the trailer was transported to a Southern California hospital in serious condition, according to the Los Angeles Fire Department.
The single-engine plane pilot died at the scene, firefighters said.
The aircraft took off from Torrance, about 20 miles to the north, with only the pilot on board, officials said. His fate was unclear.
Passers-by removed the pilot from the wreckage and a 911 dispatcher instructed them to administer CPR until first aid arrived, firefighters said.
The National Transportation Safety Board said via Twitter that it was investigating the crash of the Piper PA-32 aircraft. The tweet said it was unclear whether an NTSB investigator would travel to the scene.
The Federal Aviation Administration said it was also investigating the accident.
Media images of the wreck showed the engine and the mangled front of the fuselage separated from the rest of the plane near a transit stop.
Firefighters prevented a small amount of fuel on the ground near the plane from spreading further.