Germany’s air traffic control agency said Wednesday that it is diverting all flights away from the country’s busiest airport, Frankfurt, after a problem with Lufthansa’s computer systems caused major disruption at the German airline.

Agency spokesman Robert Ertler said all plane parking spots in Frankfurt were full because passengers and crews are unable to board the airline’s flights.

“All incoming planes are being diverted to alternative airports” such as as Munich, Nuremberg and Duesseldorf, Ertler told The Associated Press.

Lufthansa Group, which also includes subsidiaries such as Swiss International Air Lines and Eurowings, said the IT outage was caused by construction works in the Frankfurt region.

“This is causing flight delays and cancellations,” the company said. “We regret the inconvenience this is causing our passengers.”

Telephone company Deutsche Telekom later confirmed that an excavator had cut through fiber optic lines at a depth of five meters (16 feet) while working on a railroad line.

The company said parts of the destroyed line had already been repaired and the situation will improve significantly in the course of Wednesday afternoon, German news agency dpa reported.

According to dpa all of Lufthansa’s domestic flights were canceled and passengers were urged to switch to alternative forms of travel, such as trains.