German prosecutors have opened an investigation into a stampede which killed 19 people at a music festival in Germany.
Those killed died in a crush when hordes of people were pushing through a tunnel into the former freight rail yard where the techno music festival was being held.
Most of the victims - all between the ages of 20 and 40 - were found dead on the ramp and none in the tunnel, authorities said.
Authorities were not able to explain on Sunday how the tragedy happened.
Police originally said overcrowding sparked the stampede, but Duisburg's police chief later said officers had set up screening points to control the flow of people and there was room to move when the tragedy happened.
An official at the Duisberg prosecutors office says investigators are looking into "negligent homicide" in a probe "aimed at persons unknown."
German Chancellor Angela Merkel has demanded an intensive investigation.
Six foreigners, a 27-year-old woman from Australia and others from Spain, Bosnia, the Netherlands, Italy and China, were among those killed, while 342 people were injured.
NZ woman caught up in crush
A young New Zealand woman who survived the stampede says she used her lifeguard experience to try to help others.
Anneke Kuypers, 18, says she saw dead people in the tunnel, and many others unconscious on the ground.
She says some people were suffering from dehydration, and others from drug or alcohol overdoses.
