Massive power outage hits southern US and Mexico

A massive power cut caused traffic gridlock and left at least 1.4 million customers without electricity overnight into Friday in southern California, Arizona and Mexico, officials said.

Reuters/Mike Blake

Power was restored early Friday in southern California about 12 hours after the outage, San Diego Gas and Electric said in a statement.

But it warned that the grid was still "very fragile” and asked customers to “conserve electricity throughout the day Friday".

Power was also restored to 97 per cent of the Mexican border state of Baja California, Mexico's Federal Electricity Commission said.

Amid sweltering temperatures, a number of people had to be rescued from lifts and theme park rides, reports said, while two units at the San Onofre nuclear power plant tripped offline and San Diego airport cancelled all departures.

There was no suggestion that terrorism caused the outage, which comes as New York was on alert over a bomb threat ahead of the 10th anniversary of the 11 September attacks.

The outage originated in western Arizona, where a procedure by an employee of power company APS apparently triggered a wider shutdown.