A 14-year-old boy has been stabbed to death by attackers who knocked him off a moped, the Met said.
The wounded teenager was found in Bickley Road, Leyton, in Waltham Forest, at 18:30 GMT on Monday.
Detectives believe the moped had been involved in a crash with a car, after which three men got out the vehicle, stabbed the teenager and drove off.
He died at the scene and his next of kin have been informed. No-one has been arrested.
A cordon is in place and inquiries continue, the force said.
“It has now been established by detectives the boy was riding a moped that had been involved in a collision with a car,” a statement added.
“It is believed that three males got out of the car and then stabbed the victim before returning to the vehicle and driving off.”
At the scene: Greg McKenzie, BBC News
The latest victim is one of the youngest people to die on London’s streets in the last year.
His parents were here late last night being comforted by a police family liaison officer.
Locals say this area of Leyton has been getting worse, with one claiming there is an ongoing postcode war.
The police cordons are still in place, but the forensic tents are gone.
Residents who live on Bickley Road said it was not until they saw the blue flashing lights from the emergency services that they knew something had happened.
One woman, who did not want to be named, said she walked past the crime scene on her way home.
“As I was going down, I saw police on the road. When it’s that many police cars, you know something bad has happened.”
She said crime had been getting worse in the area, adding that she was hoping to move away.
“I think it’s ridiculous. Every year, every month, something’s happening – all these killings. I have kids and I don’t see them growing up here.
“Like most people, we just have to raise those funds and move out.”
Stella Creasy, the MP for Walthamstow, said she was “devastated” by the news from her constituency, describing it as a “terrible, horrific event”.
London mayor Sadiq Khan said he was “greatly saddened” to hear of the boy’s death.