Atlanta's airport, the busiest in the world, was hit by a power outage on Sunday that caused hundreds of flights to be delayed or canceled.

"Hartsfield-Jackson Atlanta International Airport sustained a power outage shortly after 1:00 pm today," the airport said in a statement.

The Federal Aviation Administration announced that it had put a "ground stop" on flights inbound for Atlanta, meaning they are held at the airports from which they were to depart.

"The FAA Tower can operate normally, however, departures are delayed because airport equipment in the terminals is not working," it said on Twitter.

Theories for what might have caused the outage circulating online included a power line cut by a construction crew and a fire near the intra-terminal train.