Shortly after noon local time the airport said in a statement that its Plane Train had returned to a normal schedule "after experiencing a computer issue" earlier Monday.
Social media posts about the situation described a chaotic scene.
"ATL airport is pandemonium with the train down and masses of people at a standstill in the underground walkway between concourses," one post said.
The airport said that airport and airline employees, as well as additional ground support, "assisted passengers in navigating the concourses to reach connecting flights, baggage claim, and gates," while train service was reduced.
There is a passenger walkway that connects the concourses.
Keagan Ilvonen, 33, made it onto his flight Monday but described the scene after security checkpoints as a "mad house."
"No staff directing, no one providing info. Just people loading off of escalators down into the train area on the ground," Ilvonen told CNN.
"Honestly the worst congestion and handling of people I've ever seen in an airport," Ilvonen said.
Tiffany King, 27, said in a message to CNN that "staff was yelling at people to walk forward but we couldn't it was a grid-locked crowd surge. It took me an hour to go from B gate to C gate."
The automated train system has been carrying passengers through the airport since 1980. It carried more than 250,000 passengers each day as of 2018, according to the airport.
The outage comes as Orlando International Airport and St. Pete Clearwater International in Florida announced the cancellation of hundreds of flights due to Hurricane Milton.
The-CNN-Wire & 2024 Cable News Network, Inc., a Time Warner Company. All rights reserved.