Two private planes flying about a mile from an airport collided, killing at least four people and raining debris down on car dealerships below, authorities said.

The small Cessnas collided Sunday afternoon near the small Corona Municipal airport and a freeway in Riverside County, about 70 kilometres southeast of Los Angeles, FAA spokesman Allen Kenitzer said.

Three of the dead were from the planes and the fourth was in a car hit by debris on the ground, Kenitzer said.

Kenitzer did not immediately know where either plane was headed or whether there were any distress calls.

The Corona airport does not have a staffed control tower, he said.

Debris fell on car dealerships, and television pictures showed that the smashed fuselage of one of the planes landed atop a parked car.

“The smaller aircraft ... just disintegrated into pieces, maybe 50 pieces coming down,” eyewitness Jeff Hardin told KABC-TV. “The other aircraft pretty much stayed intact and started spiraling down.”

Eyewitness Hector Hernandez said he saw bodies falling from the sky.

“One of them crashed into the top of a Ford Mustang, and another one fell not too far behind that one on the parking lot,” Hernandez told KCBS-TV.

Police were going through the dealerships to see if anyone was injured, Corona Police Sgt. Jerry Pawluczenko said. (AP)

Private planes collide in California, at least 4 dead as debris rains down on car dealerships