Two women were shot when a gun fired after being dropped during a police pursuit of a moped.
The Metropolitan Police said officers were pursuing two people who failed to stop in Clapham at 16:55 GMT on Friday.
The moped also collided with a member of the public and crashed a short while later, the force said.
All three people have been released from hospital as police hunt the suspects whose "reckless actions" led to the gunshots.
The Met said it had established that the shotgun went off as it struck the ground, having been dropped while the suspects fled on foot.
Two women, aged 27 and 36, who had shotgun pellet injuries, were not deliberately targeted, police said.
Det Ch Insp Gemma Alger said: "Our investigation to identify the two people responsible is at an early stage, but we will be relentless in following up every line of enquiry to arrest them.
"The suspects fled the scene on foot. Crime scenes remain in place in St Alphonsus Road as forensic searches are ongoing at premises where the suspects made off through gardens.
"The shotgun was recovered from the scene and this will also be subject to forensic analysis."
