All 1.4 million San Diego Gas & Electric customers and thousands of more Southern California Edison customers could be without electricity Thursday evening and into Friday after a "cascading event" knocked out a key facility in Arizona, an official for the San Diego utility company said.

Tens of thousands of customers in Arizona and Mexico also are affected by the power outage.

The outage has reportedly shut down San Diego Airport, sent the San Onofre Nuclear Power Plant offline and has caused major traffic delays, according to various news reports.

For updates, follow SDG&E on Twitter.

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