The helicopters hit each other in mid-air during a police exercise.
German Bild newspaper said one of the pilots was killed and four people were injured, two of them seriously.
Footage showed the two aircraft on their side in the snow.
Some 400 federal police officers were conducting a football violence training exercise when the crash happened.
An eyewitness told the NTV channel: “Three helicopters were in the air. It was a real snowstorm. Suddenly we heard a bang and someone shouted <<everybody down>>. Then there was blood everywhere. Nearby, there was a huge pool of blood.”
Pictures showed police and emergency services crawling over the wreck of one of the aircraft, apparently attending to someone inside.
Others cared for a casualty on a stretcher.
A police officer was seen walking from the scene with blood pouring down his face.
wt0c0fRh_cgImage source: Wikimedia Commons President-elect Donald Trump celebrated his election victory at the Ultimate Fighting…
Millions of voters across the US chose to return Donald Trump to the White House…
Donald Trump declares victory in the US election as he addresses jubilant supporters in Florida.…
Stocks around the world are rising as Donald Trump appears to be on the cusp…
Donald Trump has won Pennsylvania, North Carolina and Georgia and taken a lead over Kamala…
Quincy Jones, the celebrated musician and producer who worked with Michael Jackson, Frank Sinatra, Ray…