Delta Air Lines name tags seen at Delta's terminal at JFK International Airport in New York. Thomson Reuters

Delta Air Lines has resumed flight operations following a massive computer outage that crippled the airline for more than six hours on Monday.

According to Delta, a "major system-wide network outage" on Monday had delayed flights worldwide.

The widespread computer problem was caused by a power outage at its headquarters in Atlanta, the airline said in a statement.

The outage meant flights worldwide were being delayed and airport screens and Delta's website were not showing updated flight status information.

"A power outage in Atlanta, which began at 2:38 a.m. ET (6:38 a.m. GMT), has impacted Delta computer systems and operations worldwide, resulting in flight delays and cancellations today," Delta said.

Flights scheduled for departure were grounded, but those already in the air operated normally, Delta said in a statement.

Even though flights have resumed, Delta cautioned travelers to expect further delays and cancellations as the airline ramps up its operations.

"A Delta ground stop has been lifted and limited departures are resuming following a power outage in Atlanta that impacted Delta computer systems and operations worldwide. Cancellations and delays continue.



"Customers heading to the airport should expect delays and cancellations. While inquiries are high and wait times are long, our customer service agents are doing everything they can to assist. There may also be some lag time in the display of accurate flight status at delta.com, the Fly Delta App and from Delta representatives on the phone and in airport."

Delta, the world's second-largest airline measured by revenue passenger kilometers flown, operates 5,000 departures a day and is a member of the SkyTeam alliance alongside airlines including Air France-KLM.

It also partners for transatlantic flights with Virgin Atlantic, which said its flights were operating normally but cautioned that passengers should check tickets in case their flight was due to be operated by Delta as part of a code-share agreement.

The outage affected flights globally, a London-based spokeswoman for the airline said.

Passengers stuck in check-in lines in airports across the world, or aboard planes waiting to depart, shared photos and frustration at the delays on Twitter.

"1 hr.+ lines @HeathrowAirport for @Delta due to system outage," user @MITJAKE tweeted with a picture of passengers waiting to check in.

The glitch follows several high-profile computer problems faced by US airlines in recent months.

The budget carrier Southwest Airlines Co. last month had to halt departures after a technical outage, while American Airlines had to suspend flights from three of its hubs in September after technical problems.

Industry consultants say airlines face an increasing risk from computer disruptions as they automate more of their operations, distribute boarding passes on smartphones, and outfit their planes with Wi-Fi.

(Reporting by Abinaya Vijayaraghavan in Bengaluru and Victoria Bryan in Berlin; additional reporting by Sarah Young in London; editing by Gopakumar Warrier and Jason Neely)