Police were called to London Road, West Croydon, at 6.14pm on Thursday, 18 November to reports of a fight in progress amongst a group of people.
Officers attended. No suspects or victims were found.
A crime scene has been put in place.
At 7.08pm police were then called to a south London hospital after a teenage boy self-presented at the hospital with stab wounds.
Despite the efforts of doctors at the hospital, the boy died a short time later.
His next of kin have been informed.
A post mortem will be carried out in due course.
Homicide detectives from the Met’s Specialist Crime Command have been informed.
A Section 60 has been put in place in the areas of Broad Green, Fairfield, Waddon, west Thornton, Bensham Manor, Selhurst and Addiscombe West until 10.35hrs on 19 November.
Enquiries are ongoing.
Any witnesses or anyone with any information is asked to call police on 101, quoting CAD 6179/18Nov, tweet @MetCC or call Crimestoppers, 100 per cent anonymously, on 0800 555 111.