At least 90 people were injured - 40 of them seriously and 15 in critical condition. A police spokesperson said it was likely the death toll would rise further and that authorities were struggling to gain an overview of the situation.

At least eight helicopters were transporting people with serious injuries to nearby hospitals. Those with less severe injuries were being treated by rescue workers at the scene.

A lifeguard service was taking patients to the opposite side of the nearby Mangfall river for treatment.

"At the scene of the collision, one can only see debris. Rescue workers are climbing around and pulling people out," Bavarian broadcaster BR quoted a rescue worker as saying.

The man added that 10 to 15 meters at the front of each train had been completely destroyed in the collision and that both trains had partially come off the tracks.

BR said on its live blog that the commuter train were less crowded than usual due to the fact that Bavarian school children are currently on holiday for Carnival.

The reason for the head-on collision remains unclear.

The Upper Bavarian Rail Service issued a statement. "[This] is a huge shock for us. We are doing everything to help the commuters, their relatives and staff," chief executive Bernd Rosenbusch was quoted as saying.

Police were due to hold a press conference at 11:00.

Pics: (Matthias Schrader, AP)