A power cut at Atlanta's Hartsfield-Jackson international airport has led to a partial shut-down, with tens of thousands of people reported affected.
The airport is the world's busiest, handling more than 250,000 passengers and almost 2500 flights every day.
Passengers were left in darkened terminals or on board airplanes.
Power is being restored at the airport, but over 1000 flights were cancelled with hundreds of more cancellations scheduled for Monday.
Many flights scheduled to arrive from other airports are being diverted elsewhere or held at their departure airport.
In a statement, the airport confirmed they had suffered a power outage shortly after 1pm on Sunday (7am Monday NZT).
Georgia Power, who supplies the airport's electricity, said it believed a fire at an underground electrical facility was to blame for the outage.
The company said the cause of the blaze was not known.
Power was fully restored to the airport by midnight on Sunday, local time, city officials said.
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 for the rest of Sunday.
Images shared on social media showed passengers waiting in darkness. Some reported being stuck on board aircraft for six hours.
US Customers and Border Protection said international flights bound for Atlanta were diverted elsewhere.
The local police department confirmed they had sent extra officers to help the airport with the situation.
Atlanta is located within a two-hour flight of 80 percent of the US population, making the city a major port of entry into the US and a common stopover for travel within the country.