Police rushed to the scene in Dulwich at 6.30pm on Wednesday and found a man suffering from stab injuries.
The London Ambulance Service attended and despite their efforts, he was pronounced dead at the scene.
The next of kin have not been informed.
No arrests have been made and a crime scene remains in place.
At this stage, anyone with information that could assist police is asked to call 101 or tweet @MetCC and quote CAD 6306/8July.
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