German airline giant Lufthansa said Wednesday its operations were resuming hours after it was forced to cancel or delay flights over a major IT outage caused by construction work in Frankfurt.
Frankfurt airport, Lufthansa's main hub, had earlier stopped most planes from landing to avoid overcrowding as thousands of passengers were unable to board flights.
The breakdown was resolved after several hours, with flights starting to return to normal in the afternoon, Lufthansa said.
The IT systems failure had been caused by construction work in the Frankfurt region that had damaged broadband fibre-optic cables, the airline said.
Lufthansa is Europe's biggest airline group. It also owns Eurowings, Swiss, Brussels and Austrian Airlines.
The group did not immediately specify how many flights or passengers were impacted globally but Frankfurt and Munich airports appeared among those most affected.
Deutsche Telekom said four of its cables had been damaged during construction work ordered by state-owned rail operator Deutsche Bahn in Frankfurt a day earlier.
German newspaper Bild reported there had been "chaos" at Frankfurt and Munich airports because of problems with Lufthansa's check-in and boarding systems.
The airline group had urged passengers on domestic flights to book train journeys instead.
The turmoil comes as Germany is bracing for a full-day strike at seven airports on Friday, including at Munich and Frankfurt.
The stoppage has been called by the Verdi trade union, which is currently leading negotiations for better pay for public sector workers, airport ground crew and aviation security staff.
The one-day walkout is expected to lead to flight disruptions for thousands of passengers.