The discovery of an unexploded World War II bomb at Berlin's main train station was expected to paralyze the rail network for hours Wednesday, dpa reported.
Between 10 am and noon (0800-1000 GMT), long-distance trains could either be halted or diverted. The S-Bahn local overground commuter train network had not yet been affected, a railways spokesman said.
No decisions had been made but the spokesman cautioned that "passengers should be prepared for delays and detours for long distances."
A police spokesman said a decision would be made shortly on how to deal with the 100-kilogram bomb.
Dozens of World War II bombs are unearthed in Germany each year, causing wide-scale clearances before they are removed or detonated in controlled explosions.
Police discovered the bomb on Tuesday. At that time it was not immediately clear how much of the station would have to be shut down.
Road traffic could also be affected.
Late Tuesday, the area where the bomb was found was cordoned off, federal police said. Further action would be decided by state and federal police with railway authorities on Wednesday.