Delta Air Lines resumes flights after system outage

Delta Air Lines has resumed flights after a major system-wide network outage led to tens of thousands of its planes being grounded around the world.

Check-in systems, airport screens and the airline's website were affected by the problem, with airport workers having to write out boarding passes by hand.

The company, which operates flights out of Heathrow, Manchester and Edinburgh, said the ground stop has been lifted, and limited departures are resuming.

A company spokeswoman added: "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."

Social media was awash with pictures and videos of long queues and frustrated passengers.

One passenger at Heathrow told NBC News that there were "a lot of very frustrated people" waiting.

Another tweeted: "Chaos trying to check in..been in queue for 1.5 hours. You seriously need to open more desks to overcome technical hitch."

Peter Taylor added: "Still in Heathrow - should have been on 9:40 flight to Boston - waiting for news - staff apologetic, even had the captain speak to us."

Delta serves nearly 180 million customers a year, employing over 80,000 people, according to its website.