A 17-year-old girl was stabbed to death in an east London park on Friday night, Scotland Yard said.
Police were called to reports of a knife attack in the Romford area by the ambulance service at 9.25pm.
The girl was pronounced dead at the scene near St Neot's Road in Harold Hill just over an hour later.
Her next of kin have been informed and detectives from the Metropolitan Police have launched a murder investigation.
No arrests have been made and the victim has not yet been formally identified.
The death of the teenager means there have now been 18 homicides in London this year.
On Tuesday, Che Morrison, 20, who has been described by his family as a "loving" young man, was stabbed to death outside Ilford station, also in east London.
'I worry for the younger youths'
Flower tributes left near the scene where a 17-year-old girl was stabbed to death.
Police have sealed off the park and forensic officers are at the scene.
Hairdresser Ellie Best, 17, said she and her family had moved from east London and the knife crime there for the "good strong community" life in Harold Hill.
A "shocked" Miss Best said: "No one should have to get a call to say that their child has been killed.
"It is becoming more and more like central London here. Children did not fight or anything and you did not hear of people being mugged. There has never been knife crime here before - it is just in the last six or seven months.
"I worry for the younger youths. Police need to talk to them about the dangers of carrying knives because the message is not getting through."
She said the park is used by local children to "just hang out".
Police asked anyone with information about the teenage girl's death to call 020 8345 3775, tweet @MetCC or call Crimestoppers anonymously on 0800 555 111.