The stabbing took place on Grove Street in Deptford yesterday (December 31) just before 1pm.
Police were called to the scene along with paramedics, and an air ambulance was also despatched to the scene where they treated a 23-year-old man for a stab wound to the chest.
He died at the scene from his injuries.
The force has launched a murder investigation and are making enquiries.
There have been no arrests and a crime scene remains in place.
Detective Chief Inspector Sam Townsend, who is leading the investigation, said: “Our thoughts and deepest sympathies are with the victim’s family and friends during this incredibly difficult time.
“Our investigation is progressing swiftly as we work to establish the full circumstances surrounding this tragic incident.
“We understand that this will understandably cause concern within the local community.
“Please be assured that we have increased patrols in the area, and this investigation remains our highest priority.”
Anyone with information should contact police by calling 101, quoting CAD2852/31Dec.
Information can also be reported anonymously by calling Crimestoppers on 0800 111 555.
