Screaming and shouting was heard on an estate before an 18-year-old man was found with fatal stab wounds, a resident said.
The teenager was given CPR by a member of the public on the estate in Greenwich, south-east London, but died before emergency services arrived, a witness to the aftermath of the stabbing said on Tuesday.
Fireworks and shouting could also be heard before police arrived at the scene, according to another resident of the Flamsteed Estate.
“There was a bike and car that I saw speeding away after all the noise,” the witness added.
Another resident said: “I heard some screaming and shouting and thought I heard some dogs barking, but basically that is what I hear every single day.”
Police were called to a report of a disturbance in Armitage Road on Monday at 9.25pm, Scotland Yard said.
Detective Chief Inspector Richard Leonard, of the Metropolitan Police’s homicide and major crime command, said: “We know that several people reported seeing the victim in a confrontation with three other males on mopeds before an altercation in which he sustained his injuries.
“The males then rode away from the scene. I need anyone who may have information that could assist us to make contact as quickly as possible.”
Police are investigating after an 18yo male was fatally stabbed last night following a confrontation in #Greenwich – officers ask those with info to call the incident room on 0208 721 4622, or 101 quoting CAD 7560/22 October. https://t.co/XHG1gWAaOcpic.twitter.com/Iud7AcuKOX
— Metropolitan Police (@metpoliceuk) October 23, 2018
A crime scene is still in place and forensics officers are examining the area.
Formal identification of the victim has not yet taken place and a post-mortem examination will be held in due course.
No arrests have been made.
Anyone with information is asked to contact police on 101 quoting CAD 7560/22 October, or alternatively contact Crimestoppers anonymously on 0800 555 111.