UPDATE: Delta Outage: 530 more flights canceled as system pain continues
UPDATE: Delta canceled another 530 flights by Tuesday afternoon as it continues to recover from a monstrous system outage Monday that saw 1,000 flights canceled and tens of thousands of passengers stranded.
More than 200 other flights would likely be delayed throughout the day, the airline warned Tuesday morning.
It came as stranded passengers were still feeling the sting from the massive shutdown Delta said was caused by a power outage at its Atlanta base that crippled computer systems.
"Following the power loss, some critical systems and network equipment didn't switch over to Delta's backup systems," the airline said in a statement. "Delta's investigation into the causes is ongoing."
The utility company that delivers electricity to Delta disputed the airline's explanation. In a statement, Georgia Power spokesman John Kraft said that a piece of electrical equipment "on their (Delta's) system" was to blame for the outage.
"Our crews responded to the site this morning and we continue to work with the team at Delta," the statement said. "Other Georgia Power customers were not affected by the issue with Delta's equipment."
Delta said systems were fully operational late Monday but that residual delays and cancellations continued.
The airline urged passengers with travel scheduled for the morning to check the status of their flights on Delta's website or mobile app.
Delta said it was extending its offer of a refund to passengers traveling Tuesday and was also offering a $200 voucher to passengers whose flights were canceled or who were delayed for more than three hours.
PREVIOUS STORY: (NBC News) - Delta Airlines has resumed flights after a six-hour stoppage that affected flights worldwide. A power outage early Monday morning in Atlanta grounded flights and left passengers stranded at airports and on planes awaiting takeoff.
It later issued a statement confirming the outage.
"A power outage in Atlanta, which began at 2:38 a.m. ET, has impacted Delta computer systems and operations worldwide, resulting in flight delays and cancellations today," the airline said in a statement.
Due to a computer outage, flights awaiting departure are currently delayed. Flights enroute are operating normally.
"The issue is currently impacting flight status information displayed on airport screens, delta.com and some mobile and airport technology. Delta's information technology team is working to resolve the problem."
At Los Angeles, passengers on the 12:50 a.m. red-eye to JFK were taken off their plane and back into the terminal with no estimate on when they would be able to depart.
In Las Vegas, some passengers slept on the floor near departure gates awaiting updates from the airline, while at Pittsburgh a long line snaked toward the ticketing counter.
Cynthia Towles, who was at Newark Airport on her way to St. Thomas in the U.S. Virgin Islands, told WNBC: "They didn't tell us anything. I didn't get an email, I didn't get anything. Nothing."
U.S.-bound passengers at Rome's Fiumicino Airport told NBC News they had waited more than an hour to check in.
There were similar delays at Tokyo, Japan and at London Heathrow, where staff handed out bottles of water to passengers who had been waiting hours in line.
Amanda Jackson waited more than 90 minutes at Heathrow to check in for a flight to Seattle on her way to Alaska. She reported long lines at Delta counters, along with "a lot of very frustrated people."
Luciano Resende, 40, had been waiting for at least two hours at Heathrow as of 4:40 a.m. ET. He was attempting to make the trip back home to San Francisco via Seattle.
He said airline employees started to manually check-in customers for their their flights but progress had been slow. "I guess it has been a long time since they used the manual process," Resende told NBC News.