Delays could be up to three or four hours on Thursday evening, the airport said.

A relatively high number of travellers are expected at the time because of the extended upcoming weekend in Denmark following the Great Prayer Day holiday on Friday.

Some air traffic controllers have meanwhile called in sick, further compounding the staffing issue, the airport said.

“Delays are hitting extra hard today, a major travel day ahead of Great Prayer Day with 724 departures and arrivals and over 70,000 passengers in the terminals,” it told news wire Ritzau via email.

READ ALSO: Thousands of passengers experience delays at Copenhagen Airport

Capacity at the airport will be reduced by up to half of normal levels as a result of the shortage at air traffic control.

That means that the airport can, for example, receive 16 aircraft in an hour instead of the usual 30 in the worst-affected periods.

April saw over 80 flights to Copenhagen cancelled because of air traffic control staff shortages.

On Tuesday, negotiations between the air traffic controllers’ trade union and employer Naviair broke down.

Naviair wants its staff to take on extra shifts due to the shortage but has also said it has increased intake on training programmes to eventually increase the number of staff available. It will take some time before the benefits of this become tangible, however.

Copenhagen Airport said it cannot say which departures will be affected on Thursday and therefore advises passengers to go to the airport at the usual time prior to their flight.