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A half-dozen flights have been canceled and nearly two dozen others were delayed Wednesday morning after a power outage affected two major terminals at Ontario International Airport.

Southwest Airlines delayed all of its departing and arriving flights until noon, airport spokeswoman Mary Grady said. Six others were canceled.

The power outage occurred just after midnight, prompting the airport’s emergency generators to switch on for most of the grounds, except for Terminals 2 and 4, she said. It was unclear what caused the outage, she said.

Terminal 2 handles flights for United Airlines, Alaska Airlines and Delta Air Lines. Terminal 4 is responsible for American Airlines and Southwest flights.

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