Authorities say two helicopters are believed to have crashed near Berlin's Olympic Stadium during a federal police exercise, leaving at least one person dead and several injured.

Fire service spokesman Sven Gerling said his initial information was that two helicopters crashed, but he had no further details on the accident.

N-tv television and Bild newspaper said the accident occurred in snowy weather Thursday morning when some 400 federal police officers were conducting a training exercise on dealing with football violence.

Footage on n-tv showed at least one helicopter on its side on the ground.

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.