Two commuter trains crashed head-on Tuesday morning in southern Germany, killing at least 10 people and injuring 80, slamming into each other on a curve without braking after an automatic safety system apparently failed to stop them, the transport minister said..

The regional trains collided before 7 a.m. on the single line that runs near Bad Aibling in the German state of Bavaria. Aerial footage showed the impact tore the two engines apart, shredded metal train cars and flipped several of them on their sides off the rails.

Emergency services workers stand next to a body bag containing a victim near Bad Aibling in southwestern German, the scene of the head-on train collision. (Michael Dalder/Reuters)

The first rescue units were on the scene within three minutes of receiving emergency calls, but with a river on one side and a forest on the other, it took hours to reach some of the injured in the wreckage. Rescue crews using helicopters and small boats shuttled injured passengers to the other side of the Mangfall river to waiting ambulances.

Authorities said they were taken to hospitals across southern Bavaria.

"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," police spokesman Stefan Sonntag said.

Authorities had initially reported 150 injured but federal police spokesman Stefan Brandl later lowered that figure to 80, with 17 of those injuries considered serious.

Injured people were being carried by boat across the Mangfall river from the hard-to-reach crash site. (Michael Dalder/Reuters)

German rail operator Deutsche Bahn said safety systems on the stretch had been checked as recently as last week, but Transport Minister Alexander Dobrindt suggested a system designed to automatically brake trains if they accidentally end up on the same track didn't seem to have functioned properly.

However, Dobrindt said it was too early to draw conclusions.

"The site is on a curve — we have to assume that the train drivers had no visual contact and hit each other without braking," Dobrindt told reporters in Bad Aibling, near the crash scene, adding that speeds of up to 100 km/h were possible on the stretch.

Black boxes from both trains had been recovered and are now being analyzed, which should show what went wrong, Dobrindt said.

Members of emergency services hold an infusion bottle as they aid injured passengers at the crash site. (Michael Dalder/Reuters)

"We need to determine immediately whether it was a technical problem or a human mistake," he said.

German Chancellor Angela Merkel expressed shock and sent her condolences to families of the victims.

"I trust that the authorities responsible will do everything they can to clear up how this accident could happen," she said in a statement.

Drivers thought to be among dead

Nine people were reported dead immediately while a tenth died later in a hospital, Sonntag said, adding that the two train drivers 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," he said.

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.

Each train could hold up to 1,000 passengers and are commonly used by children travelling to school, but because of regional holidays to celebrate Carnival, fewer than 200 were on board in total.

"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.

Dozens of emergency services members arrived on the scene within minutes of the crash, authorities said. (Michael Dalder/Reuters)

About 700 emergency personnel from Germany and neighbouring Austria were involved in the rescue efforts and about a dozen helicopters were used.

Urgent call for blood donations

Train operator Bayerische Oberlandbahn said it had started a hotline for family and friends to check on passengers.

"This is a huge shock. We are doing everything to help the passengers, relatives and employees," Bernd Rosenbusch, the head of the Bayerische Oberlandbahn, said in a statement.

In Munich, the city blood centre put out an urgent call for donors in the wake of the crash.

The Munich Blood Donation Service, which delivers blood products to local hospitals, said on its website that there was "an acute increased need for life-saving blood products" after the accident and called for immediate donations.

The crash occurred near Bad Aibling, about 60 kilometres southeast of Munich between Rosenheim and Holzkirchen. (Google Maps)

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 driver and one passenger were killed when a train hit the trailer of a tractor in western Germany in May, injuring another 20.

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 Magdeburg in eastern Germany.

Germany's worst train accident happened in 1998, when a high-speed ICE train crashed in the northern German town of Eschede, killing 101 people and injuring more than 80.