The Molli steam train, which is popular with tourists, collided with a mobile home in the Rostock district on Sunday morning.
The two occupants of the mobile home were seriously injured, said a district spokesman for the German press agency.
In the accident at a level crossing near Wittenbeck, the mobile home was captured and dragged along for about 50 meters.
As far as we know, none of the 30 or so passengers on the Mecklenburgische Bäderbahn were injured on the train.
The clean-up work and the police investigation continued, the spokesman said.
There is a replacement rail service between the Baltic Sea resorts of Kühlungsborn and Heiligendamm.