Four men have been stabbed and six have been arrested following an incident in Camberwell.
Officers were called to playing fields outside Landor House at 5.24pm following reports of a stabbing.
According to a Scotland Yard spokesperson, the four men, all believed to be in their teens, "have all been taken to south London hospitals."
"Six males have been arrested in connection with the incident."
Police remain at the scene.
The condition of the four men is not yet known.
A witness, 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.
She added that when she walked up, she saw police officers running and a boy on the floor.
A London Ambulance Service spokesperson said: "We sent a number of resources to the scene including ambulance crews, a single responder in a car and an incident response officer.
"We treated four people at the scene and took them to hospital."
Local residents posted images of the crime scene to social media.
One person who wished to stay anonymous told the Standard they saw the aftermath of the incident.
"It must have only just happened. My bus braked and I looked up as the Police cars pulled up in front of the bus. I saw at least 10 officers run to the estate and others were already there.
"A number of officers were pushing members of the public including young people away and three or four officers were gathered a short distance away and looked like they were bending over tending to someone."
A section of Camberwell Road between Medlar Street and Wyndham Road has been closed with many local buses on diversion.
Superintendent Annmarie Cowley, of Southwark police, 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; four males are in hospital, and at this stage we cannot say how serious their injuries are. It is beyond comprehension.
“I would like to offer my reassurance to the community that officers are responding robustly; we remain at the scene and have also requested additional resources from the Territorial Support Group and Violent Crime Taskforce to patrol the area.
“Additionally, a Section 60 has been authorised from 18:30hrs to 09:30hrs on Friday, 17 August, providing officers with powers to deter any further potential trouble."
The crime scene 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.
Additional reporting by PA.