Bad Aibling, Germany (AP) -- Crews using helicopters and boats rescued dozens of people from the wreckage of two German commuter trains that crashed head-on Tuesday in an isolated part of Bavaria, killing at least 10 and leaving authorities trying to determine why multiple safety measures failed.
The trains crashed on a stretch of track running between a river and a forest about 40 miles (60 kilometers) southeast of Munich. Though the first rescue crews were on the scene in minutes, it took hours for all survivors to be airlifted and shuttled by boat across the river to waiting ambulances.
Nine people were reported dead immediately while a tenth died later in a hospital, police spokesman Stefan Sonntag said. The two train engineers were thought to be among the dead and one person was still missing in the wreckage.
"The missing person is in the part of the train where there's little hope of finding anyone alive," Sonntag said. "This is the biggest accident we have had in years in this region."
Investigators called off their search through the rubble after night fell, but Sonntag said they would resume at first light as they tried to determine why safety measures failed to stop the crash.
Two black boxes have been recovered and are being analyzed, which should show what went wrong, Transport Minister Alexander Dobrindt said.
"We need to determine immediately whether it was a technical problem or a human mistake," he said, adding that crews are still searching for a third black box.
The two trains were supposed to pass one another at a station where the track was divided, and a safety system installed on much of Germany's labyrinthine rail network was supposed to automatically brake trains that end up on the same track heading toward each other, authorities said. The two trains slammed into one another on a curve, meaning that their engineers wouldn't have seen each other until it was too late.
Dobrint said the black box data will show whether there was a signal from the automatic braking system, and if so, why the trains didn't brake until too late.
German police would not comment on a local media report citing an anonymous source that authorities believed human error might be at fault.
"Everybody is at a loss right now," said Christian Boettger, an expert on Germany's train system who works at Berlin's University of Applied Sciences.
"Trains are the safest means of transportation," he said. "There are so many security measures in place in this system that the crash is multiply mysterious."
German rail operator Deutsche Bahn said safety systems on the stretch where the crash occurred had been checked as recently as last week.
Passengers spoke of feeling hard braking then a "giant bang" as the two trains slammed into one another, tearing the two engines apart, and derailing cars near the front.
"I heard people screaming for help and heard the sound of broken glass as people were getting out," a survivor identified only as Patrick told RTL television.
He said his car was still on the tracks, but he could see the train that hit it and the first two wagons of his train were twisted and torn open.
"Bit by bit people were climbing out, some of them daubed in blood," he said. "Some were hobbling and dirty, falling into the mud."
Each train can hold up to 1,000 passengers and they are commonly used by children traveling to school at around the time the crash occurred, just before 7 a.m. However, fewer than 200 people were on board Tuesday because of regional holidays to celebrate Carnival. Schools in Bavaria were also closed because of the weeklong winter break.
"We're lucky that we're on the Carnival holidays, because usually many more people are on these trains," regional police chief Robert Kopp said.
About 700 emergency personnel from Germany and neighboring Austria were involved in the rescue effort, using about a dozen helicopters. Train operator Bayerische Oberlandbahn started a hotline for family and friends desperate to check on passengers.
"This is a huge shock. We are doing everything to help the passengers, relatives and employees," said company head Bernd Rosenbusch.
In Munich, the city blood center put out an urgent call for donations in the wake of the crash.
Germany is known for the quality of its train service, but the country has seen several other accidents, typically at road crossings. Most recently, a train engineer and a passenger were killed in May when a train hit a vehicle in western Germany, and another 20 people were injured.
In 2011, 10 people were killed and 23 injured in a head-on collision of a passenger train and a cargo train on a single-line track close to Saxony-Anhalt's state capital of Magdeburg in eastern Germany.
Germany's worst train accident took place in 1998, when a high-speed ICE train crashed in the northern German town of Eschede, killing 101 people and injuring more than 80.
Rising and Grieshaber reported from Berlin. Associated Press writer David McHugh in Frankfurt contributed to this report.