More than 1 million people in southern California and northern Mexico are without electricity after a major power failure struck just before the afternoon rush hour.

Officials blame a transmission line in Arizona which knocked out two reactors at the San Onofre nuclear power plant near San Diego, California.

Power company officials say they do not know what caused the line to fail but that they are working to get the lights back on. Officials say they do not know how long that will take.

The power failure has cut electricity to much of San Diego, parts of Arizona, and south into Mexico's Baja California and Tijuana areas.

The blackout has snarled downtown rush hour traffic, shut down streetcar service, knocked radio stations off the air, and grounded flights at area airports.