An 18-year-old man is in a critical condition in hospital after he was found with a stab wound in Montesole Playing Fields in Pinner.
The incident is believed to have happened at about 18:05hrs on Wednesday, August 26.
Officers and London Ambulance Service were called to reports of a person stabbed in the park and found an 18-year-old man with a stab wound.
London’s Air Ambulance attended the scene and the man was taken to hospital.
He currently remains in hospital in a critical condition. His next of kin have been informed.
At this early stage it is believed that the victim was with friends when they were approached by another group of youths. An altercation took place during which the victim received the injury.
There have been no arrests, and the motive for the attack is not known at this early stage.
A crime scene is in place.
The inquiry is being led by detectives from the North West Command Unit.
Detective Inspector Jonathan Newell said: “This is very serious incident that has left a young man with life threatening injuries and we urgently need information from the public.
“Anyone who was in the area of the park at the time may be able to assist. Did you see youths either going to or running away from the park?
“If you live near the park and have CCTV that might record people traveling there, let us know, we want to see that CCTV.
“Also, if you live near the area and find anything in the street, or your garden, that might have been used or discarded in this assault, call us. Anyone calling police will be fully supported and you can always call Crimestoppers if you don’t want to give your name. But please, if you have information, make that call.”
Any witnesses or anyone with any information is asked to call police on 101 or contact via Twitter @MetCC. Please quote CAD 5906/26AUG.