Even though power has been restored to the world’s busiest airport, the travel woes will linger for days.

Thousands of people were stranded Monday morning at Hartsfield-Jackson Atlanta International Airport, where more than 1,000 flights were grounded just days before the start of the Christmas travel rush.

A sudden power outage caused by a fire in an underground electrical facility brought the airport to a standstill Sunday about 1 p.m.

All outgoing flights, and arriving planes were held on the ground at their point of departure. International flights were being diverted, officials said.

The airport announced the restoration on Twitter minutes after midnight Monday, some 11 hours after the blackout began.

Georgia Power had said in a statement that the fire in the underground facility caused extensive damage, impacting substations serving the airport. The cause of the fire wasn’t immediately known.

Mayor Kasim Reed tweeted Sunday night that all passengers had been safely deplaned.

But one passenger described the situation in one terminal as “big chaos.”

The City of Atlanta said on its Twitter page that it would provide shuttle service to the Georgia Convention Center for travelers in need of a place to stay and Chick-fil-A would be provided.

Delta passenger Emilia Duca, 32, was on her way to Wisconsin from Bogota, Colombia, when she got stuck in Atlanta. She said police made passengers who were in the baggage-claim area move to a higher floor. She said restaurants and shops were closed. Vending machines weren’t working.

“A lot of people are arriving, and no one is going out. No one is saying anything official. We are stuck here,” she said. “It’s a nightmare.”

American Airlines reported only a handful of diversions and cancellations because the carrier does not use Atlanta as a hub, airline spokeswoman Alexis Aran Coello.

Hartsfield-Jackson, which serves 104 million passengers a year, is the world’s busiest airport, a distinction it has held since 1998.

The airport serves an average of 275,000 passengers daily, according to its website. Nearly 2,500 planes arrive and depart each day.