- Media reports said human error was to blame for the high-speed crash near the southern spa town of Bad Aibling, where one of the trains sliced into the other, ripping a hole in its side.
- \"My sympathy goes out especially to the families of the nine people who have lost their lives,\" Angela Merkel said in a statement.
German authorities were on Tuesday investigating how two commuter trains collided head-on, leaving at least ten dead and dozens injured, despite having been fitted with automatic braking systems to prevent accidents.
Media reports said human error was to blame for the high-speed crash near the southern spa town of Bad Aibling, where one of the trains sliced into the other, ripping a hole in its side.
Rescuers were still searching for one missing person in the mangled wreckage in a wooded area, although police said there was now little hope of finding the victim alive.
Newspaper group RedaktionsNetzwerk Deutschand (RND), citing sources close to the investigation, said a signalling station worker had manually deactivated the automatic signalling system to let the first train -- which was running late -- go past.
The second train then forged ahead on the same track in the opposite direction, before the first was able to split off where the line divides into two.
The Bild newspaper said manually disabling the signalling would have disactivated the automatic braking systems.
Regional police refused to comment when contacted by AFP. Two of the trains' black boxes have been recovered, while investigators are still looking for a third.
Police said 10 people had lost their lives in the crash just after 7:00 am (0800 GMT), while 18 people were seriously hurt and 63 others suffered light injuries.
The two drivers and two conductors were among those killed, local broadcaster Bayerischer Rundfunk reported.
German Chancellor Angela Merkel said she was "dismayed and saddened" by the accident.
"My sympathy goes out especially to the families of the nine people who have lost their lives," she said in a statement.
Completely torn apart
Blue, yellow and silver metal debris was strewn around the crash site next to a river in the state of Bavaria.
Transport Minister Alexander Dobrindt had earlier said the rail track was fitted with an automatic braking system aimed at preventing such crashes, and that investigators were probing whether there had been "a technical problem or human error".
"One train was jammed into the other and the carriage of the second train was completely torn apart," he said.
The trains smashed into each other at high speed, and the drivers probably did not see each other until the last minute because the crash happened at a curve, said Dobrindt.
Police chief for the Upper Bavaria region, Robert Kopp, said the trains were carrying about 150 passengers, fewer than on a regular work day as many people were off for the region's winter holidays.
A passenger named as Patrick B. told local radio Rosenheim 24 that shortly after leaving the station of Kolbermoor, "the train suddenly braked, there was a loud noise and the light went out".
He said he "heard people shouting for help everywhere" and together with a young man, he opened the carriage door using the emergency system.
Some 700 firefighters, emergency services workers and police officers were deployed in the rescue operation, which was complicated because the forest crash site was difficult to access. Helicopters hoisted up the injured on stretchers.
"The accident is an enormous shock for us," said Bernd Rosenbusch, who heads the Bavarian rail company BOB that operates trains on the route.
"We will do everything to help travellers, their relatives and our employees."
Christian Schreyer, chief executive of parent company Transdev, said: "We are deeply shocked and stunned that something like this could have happened. Our thoughts are with the victims and families of the victims."
After German rail was liberalised at the end of the 1990s, BOB became one of the train operators competing with state-run Deutsche Bahn.
Although it has lost its monopoly operating status, Deutsche Bahn still owns the rail network.
The accident is believed to be Germany's first fatal train crash since April 2012, when three people were killed and 13 injured in a collision between two regional trains in the western city of Offenbach.
The country's deadliest post-war accident happened in 1998, when a high-speed ICE train linking Munich and Hamburg derailed in the northern town of Eschede, killing 101 people and injuring 88.