When two trams collided in the south of Rostock, around 30 people were injured on Wednesday.
As a spokeswoman for Rostocker Strassenbahn AG (RSAG) said, one of the two drivers was seriously injured.
Three passengers also suffered serious injuries.
The first medical care took place directly at the scene of the accident.
It is estimated that around 100 emergency services from the fire brigade, medical services and police were on site.
The two trains collided in the crossing area near the town hall for reasons that were previously unknown, it said.
The rescue will take several hours.
Traffic was widely diverted.