Flights were stopped at Los Angeles International Airport (LAX) for some time on Thursday (local time) after a car gained access to the airport grounds and drove on the runway, according to media reports.
At least a dozen police vehicles surrounded the car once the incident was brought under control after a brief pursuit.
Desmond Shaw, a reporter for CBS Los Angeles, said the incident was "a really crazy one" that shut down both runways.
"There will be a huge ripple effect here after a vehicle actually breached the airport facilities and got onto the runway," he said.
"They think that it happened at Atlantic Aviation and actually came back and ended here, too."
Shaw said the LAPD would be handing the investigation over to the FBI.
Flight delays were expected, with the backlog likely to take hours to clear.
Both the LAPD and LAX have been contacted for comment.