One police officer has been pronounced dead with four others seriously injured after two helicopters collided during an anti-hooligan training exercise near the Olympiastadion in Berlin on Thursday morning.
During the exercise, some 200 police officers had acted as football hooligans arriving by train, with three helicopters transporting 20 to 25 officers to the scene, Radio Eins in Berlin reported.
The training went ahead despite heavy snowfall and, according to Der Tagesspiegel eye-witnesses, a snowdrift caused a collision as the two helicopters tried to land.
"Right now, we cannot rule out a technical defect," a police spokesman said. He also confirmed that one police officer had died in the crash and four had been severely injured.
Around 60 fireman rushed to the scene at Berlin's Olympiastadion, which has been shut down until further notice.
"We have to ensure fire protection," a fire brigade spokesperson is quoted as saying in Der Tagesspiegel. According to corresponding reports, the German interior minister, Hans-Peter Friedrich, also arrived at the scene of the crash and called for "thorough investigation".
Hertha Berlin players training close by were shocked to hear about the incident. "We did not even hear a loud bang," Hertha captain Peter Niemeyer told Tagesspiegel. "We have all been perplexed hearing about a helicopter crashing some hundred meters away."
Late in 2012, a heated debate in Germany had led to a "Safer Stadium experience" paper by the German Football League, which had been pressured by the public and politicians into taking measures against increasing violence surrounding football games in Germany.
Supporters had protested against the paper and, during three match-days in late November and early December, had voiced a silent protest against the paper, not supporting their teams for the first 12 minutes and 12 seconds of every game.