In what police are calling a “senseless” crime, the four injured teens were taken to hospital after the attack on Elmington Estate, Camberwell Road.
A neighbour has said they heard a teenager screaming for help and a group of boys running minutes before police arrived on the scene.
“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.”
Their condition is not known but another witnesses, who did not want to be named, who saw the aftermath described at least one teenager who appeared to be seriously hurt, allegedly with his stomach cut open.
Bloodied items of clothing, abandoned shoes and a large black backpack could be seen littering the floor in what appeared to be a road behind a block of flats and next to a car park.
Open first aid kits were also dropped on the floor in the cordoned off area.
“[You] can’t see much from the road as the scene was deeper inside the estate,” witness Chris Hardley told Sky News.
“There were armed police circling the area in unmarked BMW X5s and an air ambulance took off nearby/”
He added: “There is certainly a problem with stabbings in the area and it was only last month that a guy got stabbed to death round the corner.”
Scotland Yard said officers were called to Landor House, Camberwell, shortly before 5.25pm.
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.”
Police are awaiting an update on the conditions of the victims, while a crime scene remains in place.
Mr Cowley continued urged witnesses to come forward, saying: “I would urge anyone who witnessed this incident to call police and tell us what you saw; if you are concerned or worried about speaking to police, I can assure you your information would be treated in the strictest of confidence.
“If you are not a person who would speak to police but you know something, I would ask you to think of the families of those involved who tonight have a loved one in hospital.
“Please do the right thing and speak to us. Those responsible for this should not go unpunished.”
Harriet Harman, MP for Camberwell and Peckham, said on Twitter she was very concerned by the stabbing and is in contact with police and councillors.
The attack happened close to Warham Street, where drill rapper Sidique Kamara, 23, was stabbed to death on 1 August.
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.”
Any witnesses or anyone with information is asked to call police on 101 quoting CAD 5391/16 Aug.
Alternatively tweet @MetCC, or contact Crimestoppers anonymously on 0800 555 111.