An 18-year-old has been stabbed to death on a playing field in south-west London.
The teenager was fatally injured at around 4.45pm on Tuesday at the site in Craneford Way, Twickenham, the Metropolitan Police said.
He was taken to hospital but was pronounced dead just over an hour later. His family have been told.
A number of onlookers filmed what happened and police have appealed to them not to post footage on social media.
Detective Chief Inspector Vicky Tunstall said: “The incident occurred in a playing field area and was witnessed by a number of people.
“Some of those people are believed to have filmed events as they unfolded; I ask that any videos are not shared via social media to avoid causing the young man’s family any more distress at this already incredibly difficult time for them.
“Instead, please go to the police immediately. A number of people have spoken to us, but we need to hear from anyone who has information that could help.
“We’re working to establish the motive behind this tragic incident and following a number of leads. If you believe you can help us, then please make contact.”
This year is on course for a record teenage violent death toll despite overall numbers of homicides reducing due to coronavirus lockdowns.
So far in 2021 there have been 25 teenage homicides in London including the Twickenham death, compared to previous peaks in 2017 when 27 young people died, and 2008 when 29 were killed.
Chief Superintendent Elisabeth Chapple, commander for policing in south-west London, said: “Our thoughts are with the young victim and his family at this awful time.
“No young person should lose their life in London and we will do all we can to support our colleagues with their investigation.
“Local residents can expect to see an increased police presence in the area.
“If anyone has any concerns, or information that could help, I encourage them to contact those officers and tell us what they know.”
Anyone with information can contact police on 101 or Tweet @MetCC quoting the reference 5697/12OCT.
To remain anonymous contact Crimestoppers on 0800 555 111 or online.