ATLANTA (AP) — Airport operations were resuming Monday morning in Atlanta, a day after a crippling power outage left thousands stranded.

The ticketing and baggage areas were a bit backed up, but security lines were moving quickly. Most travelers were patient as the world's busiest airport recovered from the outage.

Georgia Power said a fire in an underground electrical facility caused a sudden power outage around 1 p.m. Sunday. That brought the airport to a standstill and grounded more than a thousand flights.

The utility thanked people for their patience in a tweet Monday morning and said all essential services were restored and that an investigation into the cause of the outage was ongoing.