He told officers that he had fought the masked man, who stabbed him six times in the upper body, and had managed to knock him to the ground but that the assailant was then able to run off.

The boy, a Swiss national, was rushed to hospital with life-threatening injuries. Police spokesman Patrick Maierhofer said that after speaking to him and his relatives and friends they still had no idea why he had been attacked.

The teenager told police that he left home to go to work at around 6am, and that he had the feeling he was being followed. He said that as he turned a corner he looked back and saw a man masked with a scarf and hood behind him, who then began to attack him with a knife.

He tried to defend himself but was stabbed in the chest and arms. After his attacker fled, the boy dragged himself back to the council flat where he lives with his parents, and collapsed in the hallway. His brother found him and his family immediately called an ambulance.