“From 9am, we will resume work with 100% of air traffic,” said a spokesperson for DFS, whose controllers monitor take-offs and landings at the 15 designated international airports in Germany.

It was too early to say how many flights had been affected by the disruption, the spokesperson added.

German flagship carrier Lufthansa said it had expected delays and cancellations to destinations in Germany and Europe, particularly at its Frankfurt hub, where it is the biggest airline.

It did not say how many flights could be affected. The departures board on Frankfurt airport’s website showed around 20 cancelled flights between 7.30am and 9am local time.

Earlier, the operator of Germany’s busiest airport in Frankfurt warned that the problems would impact flights across Europe.

On its website, Fraport referred to “technical difficulties” at the DFS air traffic control centre in Langen near Frankfurt, without being more specific.