A 5.4 magnitude earthquake shook parts of Southern California, reports are preliminary but no major injuries or damage have been reported.

The quake was centered near Chino Hills, about 30 miles east of Los Angeles, the U.S. Geological Survey said.

The magnitude of the quake was originally set at 5.8. But Caltech officials downgraded it to 5.4 and said they doubted the temblor would cause major structural damage.

Gov. Arnold Schwarzenegger has activated the Office of Emergency Services.