Four people have been arrested on suspicion of attempted murder after a 15-year-old boy was stabbed.
The victim is in a critical condition in hospital following the attack in Tottenham, north London, on Friday.
He was found with multiple stab wounds on Willan Road, in the Broadwater Farm estate, at around 11:15 BST.
The Met Police said two men in their 20s and a 17-year-old boy were all arrested on Friday on suspicion of attempted murder.
Another man, aged in his 20s, was arrested on Saturday morning. All four remain in custody, the Met said.
Officers believe the boy was involved in an altercation shortly before he was stabbed, possibly by someone riding a bicycle.
Police would like to speak to members of the public who gave first aid to the boy at the scene.
Det Insp Paul Ridley said: "I am keen to hear from anyone who either witnessed, or has information concerning this attack.
"The victim, not yet 16 years old, sustained multiple stab wounds and is fighting for his life.
"If you know anything about the circumstances surrounding the incident or if you witnessed it, please do come forward.
"I would also appeal to the members of the public who valiantly administered crucial first aid to the victim to come forward to my investigation team."