Met Police said officers were called to the scene in Islington after receiving reports at around 3.27pm on Saturday.
The young man was found injured in Pooles Park – off Seven Sisters Road – and was rushed to hospital.
His condition is not considered life-threatening but potentially life-threatening, said police.
Scotland Yard said a 19-year-old man has been arrested on suspicion of grievous bodily harm and is currently being held in custody.
No firearm has been recovered yet and a crime scene is currently in place, while investigations continue.
Police said a Section 60 has been issued across the whole of the boroughs of Camden and Islington.
It was in place from 4pm today and will remain so until 7am on Sunday morning.
A Section 60 allows officers in uniform to stop and search anyone, specifically to prevent and detect the carrying of dangerous instruments or offensive weapons.
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