Police have fatally shot a naked man who brandished a knife at officers in a landmark Berlin fountain.

Police spokesman Stefan Redlich said passers-by reported early Friday that a man was behaving strangely and carrying a long knife in the Neptune fountain, near Berlin's city hall.

Officers tried to persuade the man to put the knife away, but instead he started cutting himself. A policeman climbed into the water to try to stop him, whereupon the man advanced on the officer with the knife.

Another officer shot the man after he ignored calls to back off. He died at the scene.

Police say an autopsy was being conducted to determine whether the man, apparently aged around 20, died from the shot or his self-inflicted injuries.