Germany's most visited landmark Cologne Cathedral is “under stress” after a new underground train line nearby has become operational.

The first tremors were reported earlier this week when trains on Cologne’s No. 5 underground line first went to the new Dom/Hauptbahnhof station, according to The Local. 

The renowned monument of German Catholicism and Gothic architecture, which took over six centuries to complete, is a World Heritage Site. The cathedral is also the largest Gothic church in Northern Europe and gets 20,000 visitors a day.

The vibrations were confirmed by an earthquake measuring station that has five sensors inside the cathedral. The nearby philharmonic concert hall has reported similar problems. 

Cathedral officials wrote a letter to the city’s Mayor to warn him of potential damage to the one of Germany’s best known landmarks, the Kölnische Rundschau newspaper reported. 

In 2009, two people died in Cologne when the historical archive building collapsed. Mistakes made during the construction of the nearby underground train track reportedly caused the incident.

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