ATLANTA (AP) — A sudden power outage at the Hartsfield-Jackson Atlanta International Airport on Sunday grounded scores of flights and stranded thousands of passengers during one of the busiest travel times of the year.

Passengers were left in the dark when the lights suddenly went out in the early afternoon.

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Airport spokesman Reese McCranie said all airport operations were affected, and outgoing flights were halted.

Additionally, the Federal Aviation Administration implemented a “ground stop” for flights headed to the airport. That means flights heading to Atlanta were held on the ground at their departure airport.

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The U.S. Customs and Border Protection Service said on Twitter that due to the power outage, international flights were being diverted to other airports.

It took more than six hours to restore power to one concourse.

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