Mayor of London Boris Johnson said:
"It is heart breaking to see the life of another young Londoner taken so tragically. My thoughts are with this young man's family at such a terrible moment."
"This horrific incident serves as an unwelcome reminder that although violent crime in the capital continues to fall, we must continue our fight to tackle youth violence and get knives off our streets."
More top news
A nurse and writer from south London has written a poem to commemorate the Battle of the Somme.
'We are here' events in the capital captured in pictures by Londoners are trending on Twitter as the UK remembers the Battle of the Somme.
Detectives have released CCTV of man they want to speak to over the rape of a 20-year-old woman in Finchley.