A boy who was stabbed to death in Romford on Saturday has been named as Jordan Douherty.
The 15-year-old from Grays in Essex was killed after a fight started at a birthday party.
Friends screamed "he's dead" and "they've killed my best friend" as groups of teenagers "scattered" following the attack, witnesses said.
The violence broke out at a community centre on Clockhouse Lane, Romford, east London, on Saturday night after scores of youths were apparently turned away with the venue at capacity.
Three teenagers have been arrested on suspicion of murder.
A witness who gave her name only as Carol said "it was chaos out here last night" and described hearing friends of the victim screaming and sobbing. Around 9.20pm I heard a lot of noise going on. For some reason it didn't sound right. It was mostly black boys out there.
Then I heard a lad crying down the phone 'he's dead, he's dead'. He was lying down in the road, there was a lot of blood. The police were working on him, they tried their absolute damnedest with that boy last night."
Local MP Andrew Rosindell said it was "devastating" a young life had "so tragically been cut short on our streets".
Any witnesses or people with information are urged to call the incident room on 0208 345 3775 or Crimestoppers anonymously on 0800 555 111.