Police were called at about 3.15pm on Monday, 16 May to reports of a firearm discharge on Turnham Road, SE4.
Officers, including firearms officers, attended. A search of the area was carried out but there was no trace of any suspects or victims.
A crime scene is in place.
Police were called a short time later after a man, aged in his late teens, self-presented at a south London hospital with a gunshot injury. His injuries are not believed to be life-threatening.
There have been no arrests and enquiries continue.
Anyone with information is asked to call police via 101 quoting reference CAD 4414/16May.