A youth was shot dead and two teenagers received stab wounds in suspected linked incidents, the Metropolitan Police have said.
Police were called to an assault on the Pelican Estate in Peckham, south-east London, at about 1630 GMT on Wednesday.
Officers were then alerted to reports of a stabbing and while investigating found the shot youth in a stairwell at Heron House, a spokesman said.
The youth was pronounced dead at the scene. Three males have been arrested.
During their inquiries, officers had discovered a 17-year-old boy with a stab wound at an address in Gannet House.
'Not safe here'
Police were later alerted to a third victim, an 18-year-old man, after he arrived at a south London hospital, also suffering from a stab wound.
Both are said to be in a "stable condition" at separate south London hospitals.
"Officers are treating all three incidents as linked at this early stage," the a Metropolitan Police spokesman said.
The ages of the shooting victim and the arrested men have not yet been released.
A large police cordon has been put in place around the estate and officers have not let residents back into Heron House, where the victim died.
Some residents said the area had problems with gangs and anti-social behaviour.
One woman, who lives in an adjoining block and who did not want to be named, said: "I think it's pathetic. I keep my son indoors and he is 18. There's too much going on on the streets.
"It's not safe here at all. The police should be patrolling round here more often."
Another resident said: "I have lived here for a long time and experienced things like this before. It's not so much surprising because of what's happening with lots of young boys hanging around.
"About four years ago there was a shooting here and someone got stabbed outside my window about 12 months ago."