Travelers check the Delta departures board at LaGuardia Airport on Aug. 8, 2016 in the Queens borough of New York City. Drew Angerer/Getty Images

UPDATE: 5:45 a.m. EDT — About 250 Delta Air Lines flights scheduled for Tuesday morning have been cancelled by the airline as it struggles to get its operations back to normal after a power outage early Monday knocked out its computer systems worldwide. Tuesday’s cancellations are on top of nearly 1,000 flights that were cancelled Monday while many more were delayed.

Dave Holtz from Delta’s operations and customer center warned of more delays in a statement: “We were able to bring our systems back on line and resume flights within a few hours yesterday but we are still operating in recovery mode. We are sorry for what many of our customers have experienced over the past 24 hours, including those who remain at airports and continue waiting for their flights. We are doing everything we can to return our operation to normal reliability, but we do expect additional delays and cancellations.”

A travel waiver for passengers flying Monday has been extended to customers traveling on Aug. 9 as well. People whose flights have been cancelled or significantly delayed are also entitled to a compensation of $200. Customers can also claim and request refunds from the airline using this page.

UPDATE: 10 p.m. EDT — Delta Air Lines cancelled “more than 870 flights on Monday” after a power outage knocked out the airline’s computer systems world-wide. While Delta gave an estimate for delays and cancellations expected on Tuesday morning, the airline also said the numbers could go up as it worked toward getting operations back on track.

UPDATE: 7:30 a.m. EDT — While thousands of Delta Air Lines’ passengers across the U.S. and the world are still stranded, the airline has revealed the cause for its system-wide outage that has led to the grounding of all its flights. On its website, the company said: “A power outage in Atlanta, which began at approximately 2:30 a.m. ET, has impacted Delta computer systems and operations worldwide, resulting in flight delays. Large-scale cancellations are expected today.”

The airline also said customers whose flights are canceled or significantly delayed are entitled to a refund. In case of delayed flights, customers can also choose to make a one-time change to their tickets without a fee. Details for refunds and changes can be found here.

Original story:

When frustrated Delta Air Lines customers began getting in touch with the company early on Monday morning, after they faced delays in everything from checking in to taking off, the airline initially said things would be up and running shortly. But soon, in a reply to a passenger on Twitter, the company acknowledged its “systems are down everywhere.”

And that became the standard response to most complaints the airline received. Meanwhile, it put up a notification about “a computer outage” on its website that read: “Delta has experienced a computer outage that has affected flights scheduled for this morning. Flights awaiting departure are currently delayed. Flights enroute are operating normally. Delta is advising travelers to check the status of their flights this morning while the issue is being addressed.”

That the outage was nationwide was revealed in another, later tweet.

And another tweet a little later suggested the outage could be affecting operations beyond the U.S. as well.

All Delta flights awaiting departure have been delayed.