A shooting in Neasden on Monday left three people needing treatment in hospital - one with potentially life-changing injuries.
Officers were called to Dog Lane, Neasden, at 7pm following reports that a person had been shot.
They found a 17-year-old male, who has been assessed as having non-life changing injuries.
Nearby, police found a 21-year-old man with potentially life-changing injuries and a man in his 20s, who remains in serious but stable condition.
Firearms officers provided emergency aid to the victims until the arrival of paramedics. All three were transported to hospital.
Police say the suspect or suspects fled the scene.
An investigation is under way but no arrests have been made so far.
Anyone with information should call police on 101 with the reference 6551/15AUG.
Information can also be provided to Crimestoppers, anonymously, on 0800 555 111.
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