"All trains are currently being held at stations," Deutsche Bahn said, citing an outage affecting the Global System for Mobile Communications for Railways.
The GSM-R is the main communication tool between train drivers and traffic control centres.
"Our technicians are working flat out to resolve the issue," Deutsche Bahn said, adding the cause of the disruption had been identified, without elaborating.
DB didn't specify how long that might take or say how many trains or passengers were affected.
The Bild newspaper quoted DB CEO Evelyn Palla as saying that "we are now trying to get the trains into stations so that travellers can disembark."
DB said it would give taxi and hotel vouchers to passengers and, where possible, make available trains at stations for travellers to sit in. It apologised for the situation.
GSM-R, short for Global System for Mobile Communications-Railway, offers voice and data services needed to operate railways, including communication between train drivers and control centres.
According to the European Union Agency for Railways, it has been introduced across Europe since 2000 as a common standard for railway operations.
The German railway system has on rare occasions in the past halted all or most trains, but because of storms rather than for technical reasons.
with AP
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