Delta Air Lines says it has cancelled 740 flights after a power outage that began overnight knocked out its computer systems and operations worldwide.

As of 7 p.m. ET, Delta said it had operated 3,300 of its nearly 6,000 flights scheduled for Monday.  

"Systems are fully operational and flights resumed hours ago but delays and cancellations remain as recovery efforts continue." the airline said.

Tracking service FlightStats Inc. counted more than 2,400 delayed flights.

The outage began around 2:30 a.m. ET in Atlanta, the airline's base, it said on its website. A ground stop that was put in place following the outage was lifted around 8:40 a.m. ET and limited departures resumed.

A spokesman for Georgia Power told The Associated Press that the company believes the failure of Delta equipment caused the airline's power outage. He said no other customers lost power.

A Delta spokesman said he had no information on the report.

Some screens in airports displayed incorrect information that Delta flights were on time.

The airline said there be may 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.

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Travellers wait in line at Montreal's Pierre Elliott Trudeau Airport amid a worldwide grounding of Delta Air Lines departures on Monday morning. (Caroline Legault/CBC)

Flights that were already en route were "operating normally," Delta said.

In the wake of the power outage, U.S. television pictures showed some Delta gate agents writing out boarding passes by hand.

"I apologize for the challenges this has created for you with your travel experience," Delta CEO Ed Bastian said in a video. "The Delta team is working very, very hard to restore and get these systems back as quickly as possible."

The airline said it will provide $200 in travel vouchers to all customers who experienced a delay of greater than three hours or had their flight cancelled as a result of the outage. 

Canada's busiest airport, Toronto's Pearson International, tweeted about the problem Monday morning. 

Pearson's website listed Delta's morning departing flights as being on time, though some of the airline's arrivals appear to be delayed. It's unclear whether these delays are connected to Delta's outage.

A couple of hundred passengers waited at the Delta counter at Pearson, with many sitting on the floor with their luggage. 

Travellers also experienced delays at Montreal's Pierre Elliott Trudeau Airport. Delta also flies to Vancouver, Edmonton, Calgary, Regina, Saskatoon, Winnipeg, Ottawa, Quebec City and Halifax. It has a code-share arrangement with WestJet. 

'We're all stuck'0:59

Confirmation of Monday's troubles came in an official Delta account that responds to customers via Twitter. The U.S. airline declined to immediately comment by phone.

A notice on its website said passengers who have their flights cancelled or significantly delayed Monday can get a refund. The airline said it would also waive its normal change fees for passengers who rebook on later flights. 

Delta passengers can call 1-800-221-1212 or 1-800-241-4141 to rebook or get further information. The airline warned of long wait times. 

Delta is one of the world's biggest airlines, with more than 5,000 flights daily to six continents.

Last month, Southwest Airlines cancelled more than 2,000 flights across the U.S. after technology problems
prevented many travellers from checking in or boarding.

With files from The Associated Press