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

McCranie said later that emergency power was restored but not all power. Georgia Power spokesman John Kraft said the utility was working to find out the cause of the outage and restore electricity. He could not estimate when that might happen. Spokeswoman Holly Crawford said no areas outside of the airport were affected by the power cut.

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

A Southwest Airlines spokesman said in an email to The Associated Press that about 70 Atlanta departures out of 120 scheduled for Sunday were cancelled. American Airlines spokeswoman Alexis Aran Coello said three of the carrier's flights have been diverted and there have been "a couple of cancellations," but American isn't seriously impacted because Atlanta is not one of its hub airports.

Delta passenger Emilia Duca 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 to 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 at about 4 p.m., 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."

The Hartsfield-Jackson airport - serving 104 million passengers a year - is the world's busiest, 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. (AP)