Southwest, Delta, United and other airlines have planes grounded by major computer outage

Southwest Airlines Boeing 737 MAX aircraft are parked on the tarmac after being grounded, at the Southern California Logistics Airport in Victorville, California on March 28, 2019 (MARK RALSTON/AFP/Getty Images)

Flights in the US are being hit by major delays and troubles after a computer outage at many of the country's largest airlines.

Southwest, Delta, United and other airlines have been hit by the problem, which is reported to be linked to a network issue.

On Twitter, Southwest Airlines claimed that the network outage had been fixed. But problems are still ongoing as a result of the technical fault, travellers reported.

The airline described the problems as "tech-related", saying it was still working through them.

Customer service agents at affected airports would pass out information as it became available, it said.

"It's affecting our flights system wide, and we're working to see if it's affecting any other carriers this morning as well," one tweet from Southwest read. "In the meantime, once more information has been made available our Agents at the airport will be happy to disseminate it to y'all."

United Airlines wrote on Twitter that the problem was stopping it from generating paperwork.

The Federal Aviation Authority said the problem was being caused by "a flight planning weight and balance program called Aerodata".

"Mainline operations and regional operations are impacted to varying degrees," it said in a statement.

The issues come just days after a similar IT outage caused problems for US airlines. Though that problem was quickly resolved it also had a knock-on effect that saw planes across the country delayed.

And it happens amid the technical problems with Boeing 737 Max planes, which has led them to be grounded across the US.