Passengers at the world's busiest airport faced a second day of disruption on Monday after a power cut led to hundreds of cancellations.
Atlanta's Hartsfield-Jackson airport lost power on Sunday, affecting tens of thousands of people.
Passengers were left in darkened terminals or on board planes.
Power was restored overnight and a handful of passenger flights resumed just after 06:00 local time (11:00 GMT) on Monday.
Hundreds of other flights, however, were cancelled.
The airport is the world's busiest, handling more than 250,000 passengers and almost 2,500 flights every day. But during its first hour of operation on Monday morning, fewer than a dozen commercial flights departed.
A number of cargo flights had operated during the partial shutdown.
Thousands remain stranded in the airport awaiting rescheduled flights. In a statement, the airport said it had distributed more than 5,000 meals to waiting passengers.
Security processing began at about 03:30 local time, it said, but those with tickets dated Sunday would need to reprint them to pass through checkpoints.
The airport advised passengers to check the status of their particular flight directly with their airline.
A suspected fire
In a statement, the airport confirmed it had suffered a power cut shortly after 13:00 on Sunday.
Many flights scheduled to arrive from other airports were diverted elsewhere, or held at their departure airport.
Georgia Power, which supplies the airport's electricity, said it believed a fire at an underground electrical facility had caused the power cut. Officials said a piece of its switchgear could have failed and started the fire, causing cable damage.
Power was fully restored to the airport around midnight on Sunday.
Atlanta's mayor confirmed the fire's cause was under investigation, and apologised to the thousands affected.
A number of major airlines, including United, Southwest and American Airlines, completely suspended their operations on Sunday. Each had at least some flights scheduled to depart Monday.
'A lot of confusion'
Images shared on social media showed passengers waiting in darkness. Some reported being stuck on board aircraft for six hours.
One passenger, Jannifer Lee, was travelling to Minnesota from Florida with her 10-year-old pet rescue cat Penny.
Her first flight was stuck for almost four hours at the gate.
"I was hoping to have a really smooth flight, especially with a cat," she told the BBC.
"I've only ever flown with her for two or three hours before, not a 12-hour journey! I guess animals can be a lot more resilient than people."
She and thousands of others were left stranded without information from airlines about onward travel.
"There was a lot of confusion on the flight, because the national news knew more about the situation than we did," Ms Lee said.
Another passenger, Naomi Harm, was stranded on the tarmac on a Delta flight from Sacramento, California.
She told the BBC that airline staff had kept the passengers in good spirits by communicating regularly and handing out any food and drinks they had available.
She said one passenger seated close to her had been escorted down to the aircraft's cargo area to give insulin to his diabetic pet dog in the hold by an air marshal.
After almost four hours she was guided out in darkness after portable steps were found for them to disembark.
"Inside the terminal there were thousands all over, children crying," she said. "The air conditioning wasn't working and it was very hot inside."
The local police department confirmed it had sent extra officers to help the airport with the situation.
About 30,000 passengers were reportedly affected by the power cut.
Atlanta is located within a two-hour flight of 80% of the US population, making the city a major port of entry into the US and a common stopover for travel within the country.