One boy is in a critical condition and another is seriously ill after four teenagers were stabbed on a south London housing estate.
The incident on Thursday evening happened close to where a drill rapper was stabbed to death earlier this month.
Scotland Yard said the victims of the latest incident in Camberwell were between 15 and 16 years old.
Meanwhile, six boys aged between 15 and 16 are in custody after being arrested on suspicion of violent disorder and grievous bodily harm.
A crime scene remained in place on Friday morning and detectives were being assisted by specialist officers to reassure worried locals.
Witnesses said they heard a teenager crying "Help, help" before the quadruple stabbing outside Landor House on the Elmington Estate.
A group of boys were seen running minutes before police arrived on the estate after being called shortly before 5.25pm.
"Four males, aged between 15 and 16 years, were found suffering from stab wounds," Scotland Yard said.
"They were taken by London Ambulance Service to hospitals in south London, where one remains critical, one is in a serious but stable condition and the remaining two did not suffer serious injuries."
Witnesses who saw the aftermath described at least one teenager who appeared to be seriously hurt.
"It was very traumatising," said a 25-year-old woman, who did not want to be identified.
The crime scene - which was littered with bloodied clothing, trainers and medical equipment - is just a short walk from Warham Street, where 23-year-old drill rapper Sidique Kamara, also known as Incognito, was stabbed to death on August 1.
A witness to Thursday's incident said he did not think any of those involved lived on the estate.
"Ten minutes before the stabbing I saw a whole heap of youths run down that way," said the man, who asked not to be named, indicating towards the crime scene.
"Then 10 minutes later I heard people shouting and bawling out the back there.
"When I looked round the back there, I saw the youth come running from the block.
"He came to the corner and dropped.
"He was holding his belly and all of his intestines were falling on the ground."
One local mother, who did not want to be named, said she saw one of the boys carrying a blade more than a foot long.
"I could see the knife in his hand, I could clearly see the blade, it was big and that was worrying me," she added.
"My little boy is growing up around here, it's terrifying."
Another witness said she saw "lots of blood" on the ground and saw a "massive" knife lying on the floor.
"I did see a massive blade, a carving knife, it was horrifying," she added and gestured that the weapon was more than a foot long.
Another neighbour, who did not give her name, described seeing boys running on the grass opposite her flat shortly before the stabbing.
"There were four or five black boys running. All of a sudden I could hear 'Help, help'," she said.
"I have walked up and, as I did, I have seen the police running.
"One of the police officers got a first aid bag and I saw one of the boys lying on the floor."
Labour MP for Camberwell and Peckham Harriet Harman said she was very concerned by the latest stabbing and was in contact with police and councillors.
Superintendent Annmarie Cowley said: "This incident is in its very early stages and at present we cannot speculate on what the nature of it may be.
"What we can say for certain is if there needed to be an example of the utter senselessness of knife crime, then this is it."