A 16-year-old boy was shot outside a chicken shop in Tooting, south London.
Police were called to Tasty Chicken on Wimbledon Road at 21:53 BST on Thursday amid reports of shots being fired, but no suspects or injured people were found.
Just over 10 minutes later, the injured boy was found at a property half-a-mile away in Blackshaw Road.
The victim was taken to a hospital in west London with "serious injuries", the Met said.
No arrests have been made and an investigation is ongoing.
Employee Jerone Valatine said: "I heard a sound first and looked at the window and saw the bullet hole."