A 14-year-old boy has died after he was stabbed by attackers who are believed to have knocked him off his moped, Scotland Yard has said.
Officers were called to Bickley Road, Leyton in Waltham Forest shortly before 6.30pm on Tuesday to reports of a road traffic collision.
The Metropolitan Police said the boy was found with stab wounds, and detectives have established he was riding a moped which had been involved in a collision with a car.
A spokesman for the force said: "It is believed that three males got out of the car and then stabbed the victim before returning to the vehicle and driving off.
"Despite efforts of paramedics, he was declared dead at 7.09pm. Next of kin have been informed."
Police also said a crime scene is in place and confirmed The Homicide and Major Crime team have been informed.
The spokesman added: "There has been no arrest. Inquiries continue."
One man who did not want to be named described how a witness of the incident came into the premises where he works nearby, clearly horrified by what they had seen.
He said the witness told him how the teenager who was on the moped was struck by the car which was travelling in the opposite direction.
"They said they knocked him off the moped and four people got out of the car and they stabbed him seven times - there were unsurvivable wounds in his back," he said.
He said the witness recalled how the boy was possibly unconscious when he was stabbed, with his helmet thrown up to 10 metres away.
The man added: "He thought it was an accident, that somebody had knocked someone, but then he said they quickly came (out of the car).
"They beat him up, and they stabbed him, and they left."
Mayor of London Sadiq Khan tweeted: "I'm greatly saddened by news of the fatal stabbing of a 14 year old in Waltham Forest, and my thoughts are with his family and friends."
Police say all lines of inquiry remain open into the 14-year-old's death, and have not said whether they believe the murder was gang-related.