A power cut at Atlanta's Hartsfield-Jackson international airport has led to a partial shut-down and major delays to flights.
The airport is the world's busiest, handling more than 250,000 passengers and almost 2,500 flights every day.
Passengers have been left in darkened terminals or on board aeroplanes.
Many flights scheduled to arrive from other airports are being diverted elsewhere or held at their departure airport.
In a statement, the airport said they sustained a power outage shortly after 13:00 (18:00 GMT) on Sunday.
Georgia Power, who supplies the airport's electricity, said they believed a fire at an underground electrical facility was to blame for the outage.
They said the cause of the blaze was not known, but that they expected to restore power by midnight on Sunday (05:00 GMT Monday).
The flight control tower is operating normally, but a number of major airlines, including United, Southwest and American Airlines, have completely suspended their operations for the rest of the day.
Images shared on social media showed passengers waiting in darkness.
Delta Airlines said on Twitter they were working to get passengers off planes that had landed but were unable to transfer to the limited number of available gates.
The local police department confirmed they had sent extra officers to help with the situation.
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.