German rail passengers are no strangers to late or cancelled trains, but this week people aboard one intercity service were stunned to hear a new reason for why their journey came to a sudden halt: the train was deemed too dirty.

About an hour into a trip from Munich bound for Hamburg, passengers were told over the loudspeaker that their train would have to terminate in the Bavarian city of Nuremberg.

"We apologise, but we as train crew need to make a statement. This train is too dirty for us to travel any further," said the announcement, which was first reported in the Munich newspaper Muenchner Merkur.

Recounting the cut-short trip on Tuesday on LinkedIn, passenger Tom Junkersdorf posted pictures of a seemingly clean train carriage and said one passenger had asked if the announcement was a practical joke.

Confirming the incident, a spokesman for Germany's Deutsche Bahn, the state railway company, told AFP that it apologised to passengers affected and put on alternative travel within an hour of them being thrown off.

"The train was accidentally put into service without being cleaned. This is an isolated incident which we deeply regret," the spokesman said.

"We are investigating internally to see what went wrong and prevent such mistakes in the future."

Long derided in Germany, Deutsche Bahn made headlines abroad during last year's European Football Championships after fans and even players arrived at destinations hours later than planned.

After the tournament, then-transport minister Volker Wissing said that Deutsche Bahn had "overstretched itself".