The airline said early Monday that all departing flights have been delayed by a global computer system outage.
"Our systems are down everywhere," it tweeted in response to disgruntled customers.
Delta(DAL), the world's second largest airline, said the problem is a power outage at its Atlanta hub, starting at about 2:30 a.m. ET.
"Large-scale cancellations are expected today," Delta said. While flights already in the air are operating normally just about all flights yet to take off were grounded. Getting information on the status of flights was particularly frustrating for passengers.
"We are aware that flight status systems, including airport screens, are incorrectly showing flights on time," said the airline. "We apologize to customers who are affected by this issue, and our teams are working to resolve the problem as quickly as possible."
Passengers on Twitter reported problems -- including the inability to check in or being stuck on the tarmac -- from airports around the world, including San Francisco, Rome and Athens.
"The airline provided passengers with little information," said New Yorker Carly Hayes, who was due to travel from Fiumicino Airport in Rome to New York's JFK, in an Instagram quote.
Jackie Watanabe, who was due to travel from Las Vegas to Minneapolis, tweeted that the airline was handing out blankets to passengers who wanted to get some sleep on the floor of the terminal there.
"I'm not ready to go into camping mode yet, but other passengers are," she said, tweeting a photo of sleeping passengers.
Sean Carson, due to travel from Kona, Hawaii, to Los Angeles, said he had on a plane for more than four hours. He told CNN the pilot announced earlier that pizza was being delivered.
Delta did not give any details of why the computer failure was grounding flights. It would be premature to assume hacking was the cause since "most of these wounds are self inflicted," said Mary Schiavo, a CNN analyst and former U.S. Transportation Department inspector general.
Reports of delays on social media appeared to have begun around 3 a.m. ET.
Delta's problems come less than three weeks after Southwest Airlines canceled more than 1,000 flights following a system outage.
-- CNN's Donie O'Sullivan contributed to this report.
CNNMoney (Hong Kong)First published August 8, 2016: 5:20 AM ET