A teenage boy was chased through an estate by up to 15 people before being stabbed to death in a "brutal" murder, an eyewitness has said.
The victim, believed to be 17, was followed in a pursuit involving up to 15 people before being killed on the St John's Estate in Hoxton, east London.
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 witness said police arrived quickly 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."
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."
The boy is the second teenager to be stabbed to death in the capital within two days.
On Thursday night, 17-year-old Shaquan Mario Fearon died from a stab wound to his leg after a fight at a block of flats in Brockley, south-east London.