Updated | Nine killed in head-on train crash in Germany

The head-on crash happened at Bad Aibling, a spa town about 60km south-east of Munich.

Nine people were killed and around 90 injured after two passenger trains collided in the southern German state of Bavaria.

Transport minister Alexander Dobrindt, who visited the scene, said that the trains slammed into each other on a curve after an automatic safety braking system had failed.

The regional trains collided before 7 am on the single line that runs near Bad Aibling in the German state of Bavaria. Aerial footage showed that the impact tore the two engines apart, shredded metal train cars and flipped several of them on their sides off the rails. The drivers of both trains and two train guards were among those killed, police say.

The first emergency units arrived on the scene within three minutes of receiving the call. However, with a river on one side and a forest on the other, it took hours for them to reach some of the injured people in the wreckage.

Using helicopters and small boats, around 700 rescue personnel shuttled injured passengers to the other side of the Mangfall River to waiting ambulances, that took them to hospitals across southern Bavaria.

"This is the biggest accident we have had in years in this region," police spokesman Stefan Sonntag said.

German rail operator Deutsche Bahn said that it was too early to draw a definitive conclusion, but that safety systems on the stretch had been checked as recently as last week.

"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. “Black boxes from both trains had been recovered and are now being analyzed, which should show what went wrong. We need to determine immediately whether it was a technical problem or a human mistake.”

Each train could hold up to 1,000 passengers and are commonly used by children traveling to school, but due of regional Carnival holidays, 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.