In a brief statement, Amtrak said nobody was hurt when the northbound Coast Starlight train jumped the tracks shortly after 10:30 a.m. about a quarter mile east of Union Station. Amtrak described the train as "empty."
Tracks in that area are owned and operated by Metrolink, the local commuter rail agency that shares lines with Amtrak on the Los Angeles-San Diego rail corridor.
Metrolink spokeswoman Delana Gbenekama says two Metrolink trains to and from Los Angeles and Oceanside were delayed up to one hour.
Amtrak says its train to Oakland and Seattle scheduled to depart Union Station at 10:26 a.m. was running nearly two hours late.
Officials did not say what caused the train to derail.