Delta airlines cancels hundreds of flights after computer meltdown

Delta Airlines scrapped hundreds of flights and delayed many more as it digested the aftermath of a computer meltdown.

Even after the US carrier lifted its initial flight grounding order about six hours after the computer snafu struck, it warned of continued cancellations and delays, as tens of thousands of passengers around the globe were left stranded.

Travellers crowded ticket counters, stretched out on the ground in airports and tried to grin and bear it. Ticket agents were reduced to checking people in manually, news reports said.

The carrier blamed the computer problem on a power outage in its hub in Atlanta, Georgia.

Flights resumed but on a limited basis, and Delta warned the ripple effect of the computer breakdown would drag on.

"While systems are improving and flights are resuming, delays and cancellations continue," the carrier said in a statement around midday.

Teams were working "around the clock" to bring systems back online, Delta CEO Ed Bastian said in a video message from the airline's operations centre.

"As I'm sure you can appreciate, it's an all hands on deck effort," he said.

"I apologise for the challenges this has created for you with your travel experience."

Luciano Resende, 40, waiting at London's Heathrow Airport to fly to San Francisco, said it was slow going.

"I guess it has been a long time since they used the manual process," Resende told NBC News.

At Los Angeles International Airport, people waiting for red-eye flights to the east coast dozed in a crowded waiting area, many of them wrapped in red blankets.

The airline said it had cancelled 427 flights. Of 6,000 scheduled to have taken off by that time of day, it operated 1,590.

Delta has more than 15,000 flights a day along with its alliance partners.

"The timing of this problem is particularly bad because yesterday morning is one of the busiest times for both airlines and travellers as business travellers begin their work week," said Daniel Baker, FlightAware's CEO.