FAA spokesman Allen Kenitzer told The Los Angeles Times preliminary reports indicate two of the victims were operating the single-engine planes, while the other two victims were in the vicinity of falling debris. One was believed to be a pedestrian and the other was in a vehicle, Kenitzer told the Times.
A Corona police and fire dispatcher told the newspaper debris rained down on automobile dealerships.
The collision occurred just after 3:30 p.m. PST.
None of the victims had been identified by late Sunday and there was no information on the cause of the collision.
Investigators from the National Transportation Safety Board were dispatched to the scene of the crash, about a mile away from Corona Municipal Airport, and about 45 miles southeast of Los Angeles.
One of the planes was a two-seat Cessna 150, Kenitzer said. He had no information about the other craft, the newspaper reported.