ATLANTA -- Power has been fully restored after an outage at the world's busiest airport on Sunday that left thousands of passengers stranded in dark terminals and in planes sitting on the tarmac.
UPDATE: Power has been restored on all concourses. 5,000+ meals are being delivered to passengers. Trains will be operational soon.
— Atlanta Airport (@ATLairport) December 18, 2017
The ground stop for Atlanta's Hartsfield-Jackson International disrupted air travel across the United States and led to the cancellation of more than 1,000 flights in and out of Atlanta.
The outage, which affected all airport operations, started with a fire in a Georgia Power underground electrical facility, Atlanta Mayor Kasim Reed said. The electrical fire's intensity damaged two substations serving the airport, including the airport's "redundant system" that should have provided backup power, Reed said.
"We certainly understand that the outage has caused frustration and anger and we are doing everything that we can to get folks back home right away," Reed said at a Sunday night news conference.
By about 11:30 p.m. (all times EST) , power flickered back on at the atrium and several of the airports concourses, to cheers and applause.
Atlanta is the heart of the US air transport system, and the disruption led to 1,173 flight cancellations to and from Atlanta, according to flight tracking service FlightAware.
Cause of fire unknown
At 12:38 p.m., Georgia Power noticed outages in the system that were traced to a fire in underground tunnels where the airport's electric system lives, spokeswoman Bentina Terry said. The fire caused multiple faults that led to the full blackout at 1:06 p.m.
The fire's intensity prevented Georgia Power crews from immediately accessing tunnels to put out the blaze and work on restoring power, Reed added. By 3:30 p.m., crews were able to contain the fire and set to work restoring power. The cause of the fire has yet to be determined, but nothing suggests it was set deliberately, he said.
The blackout led the Federal Aviation Administration to declare a ground stop at the airport, preventing Atlanta-bound flights in other airports from taking off and causing inbound flights to be diverted.
Inside the airport, the outage cut power in the terminals, leaving passengers stranded in the dark as they stood in line at gates and security checkpoints.
People used flashlights on their phones to see where they were going, said passenger Heather Kerwin, an Atlanta resident bound for New York.
"There were a few emergency lights on, but it was really dark -- felt totally apocalyptic," she said. "I decided to get the hell out of there."
Some passengers told CNN that airport and airline staff offered no updates as hours passed, leaving people scanning their phones and tablets for information. Stores stopped serving food and passengers were evacuated to alleviate crowding.
The city of Atlanta opened the Georgia International Convention Center and offered shuttle services there for stranded passengers who needed a place to stay for the night, according to the city's verified twitter account. An estimated 30,000 people were affected by the power outage, Atlanta's mayor said.
Trapped for hours
The outage left passengers sitting in planes on the tarmac for hours.
Jodi Green's Delta flight from the Bahamas landed at 1:15 p.m. ET Sunday. Seven hours later, she was still on the plane. Green said the pilot told passengers that other flights that had ran out of fuel were evacuated before theirs. Despite the circumstances, she said, order prevailed.
"People are calm, laughing, joking," she said. "I'm amazed I've been able to sit here and not lose my mind."
CNN's Betsy Klein spent nearly seven hours in a plane on the tarmac, waiting to move. At one point, the crew said 92 planes were stuck on the tarmac, Klein said. People maintained composure as food and drinks ran out, but by hour seven, patience was wearing thin.
When she finally deplaned around 9 p.m. it was sweltering inside the airport, she said. It was unclear who was in charge and people were lying on the floor and on baggage claim belts.
The ground stop led Southwest Airlines to cancel all operations in and out of Atlanta for the rest of the day, spokesman Brian Parrish said. Customers are being offered re-bookings without fare differences, he said. United and American Airlines also suspended operations to and from Atlanta for the rest of Sunday.
Delta, which has its headquarters and largest hub in Atlanta, canceled more than 900 Delta mainline and regional flights as a result of the ground stop. The airline urged passengers scheduled to fly on Monday to check their flights, as approximately 300 flights were canceled due to Sunday's outage.
Correction: A previous version of this story misstated when the FAA grounded flights at Atlanta's Hartsfield-Jackson International Airport. Flights were grounded shortly after the airport lost electricity at 1 p.m. ET.