A murder investigation has been launched into the "brutal" stabbing of a teenage boy, police said.
The boy is the second teenager to be stabbed to death in the capital within two days.
The victim, believed to be 17, was found with stab wounds on the St John's Estate in Hoxton, in the east London borough of Hackney, late last night, after police were called to reports of an assault.
The London Ambulance Service attended, but he was pronounced dead at the scene at 11.47pm.
Police said they believe they know the victim's identity and inquiries were under way to inform his next of kin. No arrests have been made.
Detective Chief Inspector Andy Partridge, from the homicide and major crime command, said: "A young man has lost his life in a brutal manner and I am appealing to anyone who was in the area last night and witnessed this attack to come forward and speak to police."
Anyone with information is asked to call police on 020 8358 0300, or contact crimestoppers anonymously on 0800 555 111 or via crimestoppers-uk.org.
:: On Thursday night, 17-year-old Shaquan Mario Fearon died after being stabbed in the leg during a fight at a block of flats in Brockley, south-east London. Another male, 17, also suffered stab injuries but was later discharged from hospital.
Large sections of the estate remained cordoned off today, as police trawled the site for evidence.
Candles have been lit in tribute to the victim, with bouquets of flowers laid against a wall.
A 40-year-old woman, who did not want to be named, said she saw the victim being chased through the estate as she watched from the window of her nearby flat.
"There was a big chase," she said. "They ran through the estate, some on bikes, some on foot. By the end of it when he died there were about 15 people around him.
"I just heard the screams, the cries. A primal scream of death."
She added: "I could really hear it. I don't know if it was one of his friends who realised that he was dead but it was the most echoing, crying noise."
The woman said police were quickly on the scene, and acted to save the boy.
She said: "One of the policemen actually worked on him, CPR, for about 15 minutes. He really fought for him. The copper was just unbelievable."