ATLANTA (AP) - A sudden power outage brought the world's busiest airport to a standstill Sunday, grounding scores of flights in Atlanta just days before the start of the Christmas travel rush.

Passengers at Hartsfield-Jackson Airport were left in the dark when the lights suddenly went out in the early afternoon. The blackout halted all outgoing flights, and arriving planes were held on the ground at their point of departure. International flights were being diverted, officials said.

Georgia Power spokesman John Kraft said the utility was working to determine the cause of the outage and restore electricity. He could not estimate when that might happen. No areas outside of the airport were affected by the power loss.

Delta Air Lines, which has its headquarters at the airport, said more than 450 mainline and regional flights were cancelled. The airline encouraged passengers to check on the status of flights via the Fly Delta mobile app or delta.com before heading to the airport.

At Southwest Airlines, about 70 Atlanta departures out of 120 scheduled for Sunday were cancelled, an airline spokesman said in an email.

Airport spokesman Reese McCranie said some emergency power was later restored, but much of the huge facility was still without electricity.

Delta passenger Emilia Duca, 32, was on her way to Wisconsin from Bogota, Colombia, when she got stuck in Atlanta. She said police made passengers who were in the baggage-claim area move to a higher floor. She said restaurants and shops were closed.

"A lot of people are arriving, and no one is going out. No one is saying anything official. We are stuck here," she said. "It's a nightmare."

Mozell Smith, 68, of Atlanta arrived at the airport hours after the electricity went off. He was headed to Las Vegas with a sister and a friend.

"This is terrible. I wish someone would've given us a heads-up before we got to the airport," he said. "I wish there would have been better communication."

American Airlines reported only a handful of diversions and cancellations because the carrier does not use Atlanta as a hub, airline spokeswoman Alexis Aran Coello.

Hartsfield-Jackson, which serves 104 million passengers a year, is the world's busiest airport, a distinction it has held since 1998.

The airport serves an average of 275,000 passengers daily, according to its website. Nearly 2,500 planes arrive and depart each day.

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