One person died on Thursday as two helicopters collided over Berlin's iconic Olympic Stadium during a police security exercise for operations against football hooligans, authorities said.
The Berlin fire brigade said in a statement that at least one person was killed and "several injured" when the two aircraft collided at low altitude during a spring snowstorm.
German media said the casualty was a pilot.
The stadium was the venue for the 1936 Games where four gold medals for African-American athlete Jesse Owens ruined Adolf Hitler's dreams of Aryan glory for the hosts on the eve of World War II.
German media said hundreds of federal police were conducting an exercise to prepare for operations against violent football fans at the stadium.