A 15-year-old boy has died after being stabbed in west London during the morning school run.
Officers were called to reports of a fight on Blyth Road in Hayes just before 8.35am on Friday.
The victim was found suffering from multiple stab wounds and died at the scene.
The incident happened a few hundred metres away from Global Academy – a college for students aged 14 to 19 – at a time when youngsters would have been making their way to school.
The Metropolitan Police said a suspect had been detained, but provided no further details.
Tia Rek-Williams, 21, a teacher who lives nearby, said the incident had been “traumatising”.
“I didn’t see the initial stabbing but I did see past the point where the boy was on the ground,” she told the PA news agency.
“They were saying ‘come on, you’ve just got 30 seconds, hold on, keep fighting’ and as they were saying that I saw his hand drop and his eyes close. It was so traumatising.”
Ms Rek-Williams said emergency services had arrived around 30 seconds later and the boy had been treated with a defibrillator.
She said that around six people had tried to help the boy while neighbours came out of their houses and gathered in the road.
“It happened in broad daylight, a 15-year-old boy, there are so many cameras. It just shows you nothing can stop these people doing these things. This happened literally in the middle of the street, not down a back alley, in front of people’s houses. It’s just awful.”
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.”
He added that police patrols in the area will be stepped up.
Labour MP for Hayes and Harlington John McDonnell tweeted: “If anyone can assist the police with any information on this tragic incident, I urge them to come forward.”
Formal identification of the victim has yet to take place and a post-mortem examination will be held in due course, police said.
Cordons remain in place at the scene.
Anyone who witnessed the incident or has any information is asked to call police on 101, quoting reference Cad 1681/11Jun, or to contact Crimestoppers anonymously on 0800 555 111.