A 17-year-old boy has died after being found with a stab wound in northeast London.
The Metropolitan Police said officers were called to a road in Walthamstow at 9.20pm on Friday.
Paramedics treated the teenager, but he was pronounced dead at the scene.
Officers are now working to establish the boy's identity and inform his next of kin.
A crime scene is in place, but no arrests have been made.
The Met's Specialist Crime Command (Homicide) is leading the investigation.
A local resident said that before the emergency services arrived they "didn't hear anything at all that indicated violence, heard no shouting etc that we thought was odd".
Sniffer dogs were present last night, while police removed two cars, they said.
The resident added: "Police knocked on our door but we didn't see anything and we don't have CCTV.
"It is incredibly tragic and such a senseless loss of life. It feels especially shocking when it happens so close to home, and on an otherwise peaceful street."
Following the news, former Scotland Yard Detective Chief Superintendent Gerry Campbell tweeted: "How many wake up calls does London need?"
Knife crime is at its highest level in over 10 years across England and Wales - with London recording the highest number of incidents, according to a recent House of Commons report.
Any witnesses or people with information are asked to call 101 or tweet @MetCC quoting 8357/23Oct.