Police were called to the incident in Hillingdon Street around 9.15pm yesterday evening (April 14).
Paramedics tried to save a 21-year-old who had been stabbed, but he died at the scene.
Soon afterwards five men and a woman, all in their 20s, were arrested on suspicion of murder.
All of them remain in police custody while investigations are underway.
Those closest to the victim have not been found yet to be informed of the news.
Borough Commander Emma Bond leads policing in Southwark.
She said: “We understand this news is both shocking and unsettling to the community and a number of crime scenes remain in place.
“Our investigations continue and there will be an increased police presence in the area, I advise anyone in the community who has concerns to speak to their local officers.
“I would also like to appeal to the public for information.
“Please, if you saw, heard or have any footage following last night’s incident then please come forward.
“Your information can significantly help our detectives with their investigation. You can do so by calling 101, referencing CAD 7392/14APR.”
Alternatively, to remain anonymous you can call Crimestoppers on 0800 555 111.
A London Ambulance Service spokesperson said: “We were called at 4.31pm yesterday (Monday 14 April) to reports of an incident in Hillingdon Street, SE17.
“We sent resources to the scene, including an ambulance crew, a paramedic in a fast response car, an advanced paramedic, an incident response officer and London’s Air Ambulance.
“The first of our crews arrived in four minutes. Our crews treated a man at the scene. Sadly, despite the best efforts of emergency responders, he died.”
