A 15-year-old boy has died after being stabbed during a fight before school in West London.
Police were called to Blyth Road in Hayes at just before 8.35am on Friday following reports of disturbance.
The victim was found suffering from multiple stab wounds and died at the scene.
The Metropolitan Police said a suspect had been detained but provided no further details.
A Scotland Yard spokesman said: "Police were called at 8.34am to to a report of a fight on Blyth Road in Hayes.
"Officers attended the location and found a 15-year-old boy suffering from multiple stab wounds.
"Colleagues from the London Ambulance Service and London’s Air Ambulance also attended and despite their efforts, the teenager sadly died at the scene.
"A post-mortem examination will be held in due course. Formal identification has not taken place.
"A crime scene has been established and cordons remain in place at this time."
Police commander for Hillingdon, Chief Superintendent Peter Gardner, said: “I am deeply saddened to hear of the tragic loss of a child’s life to knife crime in Hillingdon.
“This incident, that claimed the life of a 15-year-old boy, took place during this morning’s school run.
“A family has been devastated and the effects of this terrible incident will reverberate throughout our communities.
“As a parent of a teenage boy myself, I cannot imagine the pain the family is going through and I offer our full condolences and support.
“Police patrols today and throughout the weekend have been enhanced in order to provide a more visible and reassuring presence for the public. If you have concerns please do approach my officers and speak with them.
“Local officers will support our Homicide detective colleagues and I thank the public for their patience as officers deal with the crime scene and local enquiries.
The boy is the second teenager to die in London in 24 hours following a fatal stabbing in Streatham, south London on Thursday afternoon.
Seven people have been arrested in connection with that incident.