NEW YORK (CBSNewYork/AP) — Delta says “limited” flights have resumed following a computer shutdown that stranded thousands of passengers around the world Monday morning.

CBS2’s Christine Sloan reported hundreds of flights were canceled as delays range from two to seven hours.

As of 7 p.m., Delta officials said 3,340 of its 6,000 flights worldwide had taken off and landed and more than 740 flights had been canceled.

In a statement on its website, Delta warned customers heading to the airport that delays and cancellations would continue.

“While inquiries are high and wait times are long, our customer service agents are doing everything they can to assist,” the airline said.

In an earlier statement, Delta said “large-scale cancellations are expected” Monday.

The global ground stop was lifted around 8 a.m., hours after the outage, which began in Atlanta around 2:30 a.m., impacted all of Delta’s computer systems and operations, the airline said.

Delta said it’s going to take a couple of days to get back to normal as many are asking where was Delta’s back-up system to protect its computers.

“I think it’s kind of silly,” said June Reyes of Henderson, Nevada. “I work in a hospital and we have back-up generators and they have to be tested regularly.”

Delta passed out water bottles at Newark Liberty International Airport. Joan Barnard and her family were stranded at the airport.

“Some of us are standing in line so we can go up there and get on another flight,” she said.

Flights that were already in the air operated normally, but over the next several hours, only a handful of flights took off instead of the usual hundreds, according to flight-tracking services.

People all over the world were affected and pictures posted on Twitter showed passengers stuck at airports as lines at terminals began to grow.

“For an airline to have its computer system go down globally, that’s really unacceptable,” one passenger at LaGuardia Airport told CBS2’s Janelle Burrell.

“We went through the whole process just like normal. By the time I got to the gate, the attendants were really frustrated. All I asked was is LaGuardia boarding and the guy basically looked at me like I had three heads,” another passenger told WCBS 880’s Marla Diamond.

“The lack of information is ridiculous,” another passenger at Newark Airport told 1010 WINS’ Glenn Schuck. “I fly probably 100,000 miles a year and usually, typically, they will be able to give you a time frame. There’s no time frame given.”

A typical response to Delta’s customers complaining about their service was: “Our systems are down everywhere. Hopefully it won’t be much longer.”

Delta CEO Ed Bastian apologized for the incident.

“We’ve got Delta teams working around the clock to restore our systems capabilities,” Bastian said. “As I am sure you can appreciate it, it’s all hands on deck effort.”

National Association of Airline Passengers, a passenger advocacy group, said Delta’s system shouldn’t be this vulnerable.

“It’s surprising that the airline did not have a back-up to their computer system that a simple power failure in Atlanta could take them down worldwide,” said Douglas Kidd, executive director of the group. “You have at any given time backups to your backups, that’s why we have co-pilots on aircraft.”

In June, a computer glitch on Southwest Airlines delayed hundreds of flights. United also grounded flights this summer when a router couldn’t send flight plans to pilots.

“The demand for power is increasing, but the infrastructure is pretty much the same as it has been for some time,” Kidd said.

The back log of flights left crippling effect on the the airline’s schedule as their customers scramble to make alternate plans.

“I’m heading back to Atlanta and then I have another Delta flight tomorrow morning, so this is a domino effect,” said traveler Annella Drake.

The airline said it has published a waiver for customers traveling on Monday through August 12, saying if your flight is canceled or significantly delayed, you are entitled to a refund.

Delta is also offering a $200 flight voucher for passengers who experienced a cancellation or a delay of three hours or longer.

To check the status of your flight, click here.

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