The Met Police confirmed they were called to reports of a disturbance on Edenvale Road, in Mitcham, Merton, at around 4.47pm this afternoon (March 21).
Police officers who attended the scene alongside London Ambulance Service (LAS) found a man who had been stabbed in the chest.
The man, whose age is not yet known, was taken to a South London hospital and police are awaiting an update on his condition.
A second man subsequently self-presented at hospital with a stab injury.
His condition has been assessed as non-life threatening.
Police confirmed six men have been arrested and taken into custody.
A crime scene remains in place as police continue their enquiries.