A three-hour police standoff between ended with officers storming the premises and finding a man "unresponsive".
Police said they were called to a "disturbance" in Grove Vale, East Dulwich on Tuesday morning and, after a three-hour siege, officers forced their way into the premises and found the man.
A Metropolitan Police spokesman said: “At 10.20am, officers from the Territorial Support Group forced entry to the premises and found an unresponsive male.
“An ambulance crew is at the scene and is treating the man.”
It was initially reported that the standoff involved hostages but the Met denied this.
Police said they were called at around 7am to reports of a "disturbance" in Grove Vale.
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"Officers are currently speaking to a man in a property who is refusing to come out," a forces spokesman told HuffPostUK when the incident was in progress.
He confirmed the London Fire Brigade and London Ambulance were there and officers had put up a cordon.