A 16-year-old boy who was murdered in north-west London was being chased by a group of people before he was stabbed multiple times, the Metropolitan Police said.
The victim was heard shouting “help me” before he collapsed near the doorstep of a family home, according to an eyewitness.
The boy died at the scene in Munster Square, Camden after police were called at around 11.10pm on Monday.
Three young men were heard “screaming and laughing” as they pursued him with a machete, according to the eyewitness, who did not want to be named.
She added: “I was just in my room and all I heard was screaming and shouting.
“Through my bedroom window I could see everything.
“We just saw the three boys holding him. He said ‘help me, help me, help me’.
“He collapsed on the floor and then it was quiet.”
The victim’s stomach was visibly bloodied, she said.
The suspected attackers are thought to have fled in a car, according to the force.
Detective Chief Inspector Paul Healy said: “We believe the victim was chased around the square by a number of suspects prior to being stabbed a number of times.
“The suspects made off in a vehicle which was discovered burnt out nearby.
“Another vehicle believed to be involved in the incident was also found burnt out some distance away.”
“We have a dedicated team working relentlessly to track down those responsible.
“We’re reviewing CCTV, knocking on doors and completing other enquiries to build a clear picture of the events last night.
“We’re still in the early stages of our investigation and we are urging those who have information to do the right thing and speak to us.
“I am sure that others will have seen something last night around the Munster Square area, I am also interested in those who may have dash cam footage in the area at the time.”
A man who lives near to where the body was found, who did not want to be named, said the square has recently become a hotspot for drug taking and groups of men regularly gather there.
A crowd of emergency services and members of the local community were at the scene following the attack, he added.
At the scene on Tuesday afternoon, a large police cordon remained in place, and stretched across a number of nearby roads.
Flowers have been left at the scene as a tribute to the young victim.
In Munster Square, a first aid bag could be seen on the pavement close to a bollard, with white sheeting on the ground outside one of the flats.
Any witnesses or anyone with information is asked to call police on 101, quoting incident number CAD8433/12Aug.