“We sincerely apologise to our customers for the inconvenience this morning,” the airline said.

“It’s all hands on deck as our team is working diligently to get customers where they need to go as quickly as possible.”

Departure boards at major US airports are still showing delays of up to two hours for some flights as the airline recovers from the nationwide issue, but real-time tracking website Flightradar24 shows planes taking off again at a number of major US travel hubs and most flights are departing on time.

Passengers reported on social media being stuck on the tarmac or at gates as flights were impacted by the outage for around an hour.

Some passengers were also told to disembark from their planes.