Seven people have been arrested on suspicion of attempted murder and grievous bodily harm.
A man suffered a serious head injury after the assault outside flats in the Grahame Park Estate, Colindale on Friday night.
Police officers were called at 10.17pm and believe the man was assaulted outside Mercury Block on the estate.
The identity of the injured man is still to be established, but he is believed to be local and aged in his late teens to early 20s.
Five 16-year-old boys and a 15-year-old boy were arrested on suspicion of attempted murder, and a 19-year-old man was arrested on suspicion of grievous bodily harm.
All remain in custody at a north London police station.
Anyone with information can call 101 or Crimestoppers anonymously on 0800 555 111.
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