A 20-year-old man has died and two others have been injured in a stabbing outside Parsons Green Tube station.
Police were called at 7.37pm on Monday to reports of an incident outside the Underground station, where 30 people were injured in a terror attack last month.
Scotland Yard said a murder investigation had been launched and one of the injured men had been arrested in connection with the incident.
The arrested man was taken to hospital and has since been discharged. He remained in custody, officers added.
A London Ambulance Service (LAS) spokeswoman said it received a call at 7.38pm to an incident near the station.
She said: "We sent two ambulance crews, a first responder in a car and an incident response officer to the scene. A team from London's Air Ambulance was also dispatched to the scene by car.
"We treated three patients at the scene. We have taken two patients to hospital as a priority. Sadly one patient died at the scene."
Parsons Green Lane and the station have been closed by police and cordons were in place.
A woman was heard crying after people, who appeared to know the victim, were later ushered inside the cordon.