A 16-year-old boy was rushed to hospital after being stabbed in a shopping street in Croydon.
Police said the victim was taken to a south London hospital where his condition was assessed as non life-threatening.
A Met Police spokesman said: “A crime scene is in place and an investigation is under way.
“Anyone who witnessed the incident or who has other information and has not yet spoken to police should call 101, giving the reference 4643/09NOV.
“Information can also be provided to Crimestoppers, anonymously, on 0800 555 111.”