Delta airlines
© Joshua Lott / Reuters
A worldwide system failure has been reported by Delta Air Lines. Social media users have posted photos showing long lines of passengers waiting to check-in at airports.

"Delta has experienced a computer outage that has affected flights scheduled for this morning. Flights awaiting departure are currently delayed. Flights en route are operating normally. Delta is advising travelers to check the status of their flights this morning while the issue is being addressed," the airline said in a statement.

According to Twitter accounts, passengers are stuck at Heathrow Airport in London, Málaga Airport in Spain, Keflavík International Airport in Reykjavík, Iceland, Amsterdam Schiphol Airport and Rome Ciampino Airport.

Delays have also been reported at Seattle-Tacoma International Airport San Francisco International Airport, Sarasota-Bradenton International Airport in Florida and NYC LaGuardia Airport.

"We're currently experiencing system issues and working to resolve it asap," Delta told another passenger on Twitter.

The failure reportedly caused problems with checking into and boarding Delta flights.

The airline had to ground flights scheduled to leave Monday.

"Flights awaiting departure are currently delayed. Flights en route are operating normally. We appreciate your patience," the airline wrote on Twitter.

The airline later explained that a power outage in Atlanta "has impacted Delta computer systems and operations worldwide, resulting in flight delays."

"We are aware that flight status systems, including airport screens, are incorrectly showing flights on time. We apologize to customers who are affected by this issue, and our teams are working to resolve the problem as quickly as possible."

Delta Air Lines is the second-largest airline in the world, topped only by American Airlines. In 2015, it came in third for amount of passengers, with almost 140 million traveling on the airline.