Police were called to Miall Walk, SE26, shortly after 9.30pm on Friday to reports of a stabbing.
Officers and the London Ambulance Service attended the scene and found a 19-year-old man suffering stab injuries.
Despite the efforts of emergency services the man died at the scene a short time later. The man’s next of kin have been informed, but formal identification has not taken place.
Police said a post-mortem examination will be carried out in “due course”.
No arrests have been made.
Detective Chief Inspector Chris Wood said: “Met officers have been working through the night to commence what will be a rigorous investigation into the death of this young man. Police cordons remain at the location as a painstaking forensic examination gets under way.
“The victim’s mother has been to the scene and has met with officers. She and other family members will be provided with ongoing support, and my heart goes out to her as she faces up to the first day of the rest of her life without her son.
“I can assure her, and indeed all Londoners, of my total commitment to finding the person or persons responsible for this murder and bringing them to justice.
“The support of the local community, and of anyone who may know anything about this tragic incident, will also be crucial. If you have any information, please get in touch.”
Anyone with information that may assist the investigation or any witnesses who are yet to speak with police are urged to call 101, ref 8005/25jun. To remain anonymous, please contact Crimestoppers.