ATLANTA • One of the heaviest travel weeks of the year began with the cancellation of more than 1,000 flights at the world's busiest airport in Atlanta.

A power outage that lasted nearly 11 hours on Sunday left passengers stranded in darkened terminals or in aircraft idling on tarmacs.

"Still on plane for going on fifth hour," tweeted Mr Anthony Foxx, former transportation secretary under president Barack Obama. "Whatever the cause, it feels like this one was compounded by confusion and poor communication."

The early afternoon outage paralysed operations at the Hartsfield-Jackson Atlanta International Airport until Sunday night, before power was restored near midnight.

But the incident continued to wreak havoc on holiday travel plans for thousands of people who were hit by the airline cancellations that extended into yesterday.

Delta cancelled about 1,200 flights as a result of the outage over the two days. United Air Lines yesterday also warned on social media that air travel would be affected.

The incident led the Federal Aviation Administration (FAA) to ground flights bound for Atlanta. American Airlines and Southwest Airlines were also among the major carriers that suspended operations at the airport. Southwest itself cancelled 70 departures.

Georgia Power, the utility that provides electricity to the sprawling airport, said the failure was linked to a fire in an underground facility that damaged substations serving Hartsfield. "No personnel or passengers were in danger at any time," the company said.

The blaze, possibly started when a piece of gear failed, damaged access to a backup system, the company said. All passengers had safely disembarked from the affected aircraft about nine hours after the outage began, Atlanta Mayor Kasim Reed said on Twitter.

Photos and videos posted on social media show passengers huddled in partial darkness inside crowded terminals. Some said they sat on planes for hours.

The FAA said earlier that it had boosted the number of staff to handle the expected resumption of commercial traffic yesterday. Some stranded passengers found lodging in local hotels, and the city was providing shelter at the Georgia International Convention Centre.

Following the outage, airport officials said on social media that they had served more than 5,000 meals to passengers. "We're just focusing on the comfort of our passengers," Mr Reed said at a news conference on Sunday. "We know they have had a very, very long and difficult day.

Delta, hit hard because of its hub in Atlanta, said customers flying to or from the airport could make a one-time change to travel plans within certain guidelines.

Other airlines also offered waiver for flight changes. Delta said its flight schedule in Atlanta was expected to return to normal by yesterday afternoon.

For all carriers, more than 1,170 flights in or out of Hartsfield were scratched on Sunday, airline tracking service FlightAware said.

The airport serves on average about 275,000 passengers each day, according to its website.

REUTERS, AGENCE FRANCE-PRESSE