One person killed in double helicopter crash near Olympic Stadium in Berlin

According to reports the helicopters hit each other during a police exercise

Two helicopters have clipped each other in a mid-air collision near Berlin's Olympic Stadium, leaving one person dead and several injured.

Authorities say emergency services attended the scene of the crash which has left at least one person dead. According to reports the helicopters hit each other during a police exercise.

The German newspaper Bild said one of the pilots was killed and four people were injured, two of them seriously.

Footage from the scene showed one black helicopter on its side in the snow. Reports say police were conducting football violence training when the accident happened in snowy weather.

Some 400 federal police officers were conducting a training exercise on dealing with football violence. Federal Police spokesman Frank Brochert confirmed there "was an incident during an exercise" and that emergency crews were on the scene. He had no details about the accident.

Eyewitness Johannes Malinowski said on n-tv television that he saw three helicopters approaching and that the snow on the field was being kicked up by the aircraft, so "you couldn't see a whole lot anymore".

Then "there was a big bang and someone shouted, 'everybody on the ground,"' he said. "And then we looked up and there was blood on the ground."

The police were conducting a training exercise on dealing with football violence.

The Olympic Stadium is home to the Hertha Berlin football club. It also hosts the annual German Cup final and was the venue for the 2006 World Cup final.