Electricity to Atlanta’s airport—one of the world’s busiest—was restored hours after an outage forced Delta Air Lines Inc. and other carriers to cancel over a thousand flights and divert many others. The city’s Mayor Kasim Reed tweeted about the restoration, while the local utility in charge of the supply, Georgia Power Co., said in a statement Monday that all “essential activities” at the airport, including all concourses and flight operations, have power. The electricity went out after 1 p.m. local time Sunday, prompting the Federal Aviation Administration to issue a stop on all flights heading to Hartsfield-Jackson Atlanta International Airport. Aircraft were held at their departure airports Sunday afternoon, and planes in the air were being diverted to other cities, the airport said. Atlanta-based Delta dropped a total of 900 mainline and regional flights because of the outage, and as of 7:15 p.m., it had scrapped the rest on its Sunday schedule out of the city. Georgia Power said a fire caused “extensive damage” in an underground facility, though no passengers or workers were in any danger. In a Sunday night press conference, Mayor Reed said the intensity of the fire damaged the switch that would have allowed the built-in backup power systems to take over. Complicating matters further, the heat and fumes in the underground tunnels prevented Georgia Power crews from starting work on repairs for some time and lengthened the outage, he said. There is “no evidence to suggest the fire was caused deliberately,” Reed said. Delta was working to get passengers off aircraft on the ground that were unable to park at Hartsfield-Jackson’s gates because of the electrical failure, the company said in a statement on its website earlier. Delta expects to operate a “near-full” schedule on Monday. Southwest Airlines Co. said it canceled about 70 flights out of Atlanta, out of about 120 total scheduled departures on Sunday. Flight tracking service FlightAware reported 1,099 flights to or from Atlanta had been canceled as of 7:15 p.m. Late Sunday, the Atlanta Police Department had dispatched extra officers to help with crowd control at Hartsfield-Jackson and handle traffic around the airport, APD Officer Lisa Bender said in an email. Lighting inside the facility was limited, Delta spokesman Michael Thomas said. At one point Sunday, Delta had as many as 100 planes that were unable to park at gates, Thomas said. The airline used portable staircases to unload passengers from some planes, while there were built-in staircases in the rear of other aircraft, he said.