A male was found with a stab injury to his hand in Swiss Cottage on Tuesday night.
Scotland Yard said officers attended reports of the incident in Finchley Road shortly after.
A Met spokesperson said: "A male was found suffering from a serious knife injury to his hand. He was taken to hospital; his condition is not believed to be life-threatening."
The police said there had yet to be any arrests, but that enquiries into what happened are ongoing.
Rashid Iqbal, chief exec of the Winch youth centre in Swiss Cottage, said this was "sad news" and tweeted on Wednesday: " [Our] youth team and local partners are out in the area talking to young people in the community, offering reassurance and advice.
"If you see us, please say a physically distanced hello. We're a safer community when we are socially connected."
Anyone who has information that could assist police is asked to call 101 and use the reference CAD 9092/2 Feb.
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