A 15-year-old boy is in a "critical condition" after being stabbed in the stomach in Swiss Cottage on Wednesday afternoon.
The Met said officers were called at 4.31pm on June 23 to reports of a stabbing in Dobson Close.
Police officers and paramedics – including from the air ambulance – treated the teenager who was found with a wound to his abdomen.
A Met spokesperson continued: "The teenager was taken to hospital for treatment; he remains there in a critical condition.
"Enquiries are ongoing to establish the full circumstances of the incident."
A 15-year-old boy has been arrested on suspicion of causing grievous bodily harm with intent and is in custody at a police station in north London.
The Met is asking for anyone with information to call 101 or tweet @MetCC with CAD reference 5349//23Jun.
Witnesses can also contact Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org.
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