Lufthansa logo is seen displayed in this illustration taken.

An IT failure at Lufthansa (LHAG.DE) stranded thousands of passengers and forced flights to Germany’s busiest airport to be cancelled or diverted on Wednesday, with the airline blaming botched railway engineering works that damaged broadband cables.

More than 200 flights were cancelled in Frankfurt, a vital international transit hub and one of Europe’s biggest airports, a spokesperson for operator Fraport (FRAG.DE) said.

Lufthansa later said all its IT systems were up and running again and that it expected Frankfurt flights to return to normal on Thursday.

Scores of flights were also delayed, data from FlightAware showed. Photos and videos from several German airports showed thousands of passengers waiting to be checked in.

“We wanted to go to the wizard convention in England, in Blackpool. And now we are stranded here,” Alexander Straub said at Frankfurt airport. “We have eaten some pretzels and are still waiting,” said his fellow passenger Marc Weidel.

Lufthansa and Germany’s national train operator blamed the problem on third-party engineering works on a railway line extension that took place on Tuesday evening, when a drill cut through a Deutsche Telekom (DTEGn.DE) fibre optic cable bundle.

That caused passenger check-in and boarding systems at Lufthansa to seize up on Wednesday morning and prompted German air traffic control to suspend incoming flights, though these have since resumed.

Other airports also reported cancellations as a knock-on effect. Paris Charles de Gaulle airport said two flights had been axed and a further two flights had had to turn back around.

Amsterdam’s Schiphol Airport, among the world’s busiest, reported one cancellation of a flight to Frankfurt.