Manham at the world’s busiest airport.

Atlanta Hartsfield- Jackson International airport lost power on Sunday around 1 p.m.

The cause of the power outage was unknown at first. Thousands of passengers were stranded at the airport and all flights in and out of Atlanta was cancelled or delayed causing a major strain on airports all around the world. The power was finally resorted 11 hours later.

When the power went out, many passengers had no idea what happened. Many people went to social media for information. A ground stop in Atlanta disrupted air travel across the United States and led to cancellations of more than 1,000 flights in and out of the airport. 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. 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.

An estimated 30,000 travelers in the airport were impacted. People used their phone flashlights to navigate around the dark airport. 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.

The outage left passengers sitting in planes on the tarmac for hours. All flights getting ready to take off had to stop. One Delta flight was stuck on the runway for over seven hours and they couldn’t use the bathroom as there was no running water. 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. United and American Airlines also suspended operations to and from Atlanta for the rest of Sunday. Delta, which has its headquarters in Atlanta, canceled more than 900 flights Sunday. The airline urged passengers scheduled to fly on Monday to check their flights.

At midnight, the power was restored. TSA checkpoints were opened shortly after and operations were back to normal, but long lines and anxious passengers were waiting to get on planes. Chick-fil-a even opened on Sunday to pass out food and water to travelers in the airport that have been stuck there for many hours in the dark. The first flight took off from Atlanta at 12:56 a.m. on Monday after an 11 hours standstill. People say it may take days for the airport to return to a normal schedule and other airports may be impacted by the incident.