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. 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.

Georgia Power spokesman John Kraft said the utility was working to find out the cause and restore electricity. He could not estimate when the power might be restored.

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.

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.