Police were called to Granville Road, NW6, at 11.22pm on Friday, 14 July following reports of a fight in the street and a person stabbed.
Officers attended along with paramedics from the London Ambulance Service.
Despite the efforts of emergency services, a 17-year-old male died at the scene. His family has been informed.
A post-mortem examination will be held in due course. Formal identification has not taken place.
Another male also believed to be 17 years old, was treated at the scene before being taken to the hospital. A woman, aged in her early 20s, received hospital treatment for an injury to her hand.
Detectives from the Specialist Crime Command are investigating.
Detective Chief Inspector Mark Rogers, said: “We believe that there was a fight following a birthday party, which would have been attended by a number of people. I would urge anyone who was there, and who has not yet spoken with officers, to please come forward. It is vital that we establish what happened.
“I would also ask that anyone who may have captured any of last night’s events on their phone to also contact officers.”
A crime scene remains in place. There have been no arrests at this time and enquiries continue.
Chief Superintendent Dan Knowles, in charge of the North West Command Unit which polices Brent, said: “I know that the community will be shocked by this incident in which a young man has lost his life.
“We shall be working with our colleagues from Specialist Crime to ensure that this investigation proceeds as quickly and thoroughly as possible.
“Local residents can expect to see an increased police presence in the area and I would encourage anyone with information, or concerns, to speak with them.”
Anyone with information is asked to call police via 101 quoting reference CAD 8929/14Jul. To remain anonymous contact Crimestoppers on 0800 555 111.
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