Two passenger trains have crashed near Bad Aibling, south east of Munich, with police claiming at least four people have died and many more injured.
One of the trains was apparently derailed in the crash and rescue teams are trying to free people still trapped in the wreckage.
Reports state that 15 of the casualties are in a critical condition with around 40 people seriously hurt.
"This is the biggest accident we have had in years in this region and we have many emergency doctors, ambulances and helicopters on the scene," another police spokesman, Stefan Sonntag, told the Associated Press news agency.
The accident occurred on the popular line between Rosenheim and Holzkirchen shortly before 07:00am.
The cause of the collision is not yet known.
Roads around the scene have been closed and the railway line between Holzkirchen and Rosenheim is suspended.