Video report by ITV News Correspondent Neil Connery
Four unrelated knife murders of young men in London - three on New Year's Eve and a fourth in the early hours of New Year's Day - are being investigated by police.
The stabbings happened between 11.30am on New Year's Eve and 2.35am on New Year's Day in north, east and south London. None of the murders are being treated as linked, Scotland Yard said.
A fifth man who was also stabbed in the New Year's Day incident is in a critical condition in hospital.
All the victims are aged between 17 and 20.
The Metropolitan Police said that:
At around 11.30am on December 31, an 18-year-old man was stabbed in Larmans Road, Enfield. He died at hospital that evening.
At around 7.35pm on December 31, a 20-year-old man was fatally stabbed in Memorial Avenue, West Ham.
At around 11.40pm on December 31, a 17-year-old male was fatally stabbed in Norwood Road near the junction with Station Rise, Tulse Hill.
At around 2.35am on January 1, a 20-year-old man was fatally stabbed in Bartholomew Court, Old Street.
Five men have been arrested in connection with the murder in Enfield but no arrests have been made in the three other cases.
Commander Neil Jerome, of the Met's Territorial Policing Command, said: "It is heart-breaking that, at a time when so many of us are contemplating what lies ahead in 2018, four families are dealing with the grief of losing a loved one to senseless violence and the callous use of knives as lethal weapons.
"I can assure Londoners - and the families and friends of the four males killed and the fifth who remains in hospital - that detectives will work tirelessly to bring to justice those responsible for such despicable acts of violence.
"I would urge anyone with information about these attacks, and more generally about anyone who routinely carries a knife, to urgently pass that information to police or Crimestoppers.
"If you've hesitated to do so before, then these four tragic deaths at the start of a new year may persuade you to act now to make London safer for your family and friends in 2018."
Anyone with information can call police on 101. To remain anonymous call Crimestoppers on 0800 555 111 or contact them via the Crimestoppers website: crimestoppers-uk.org.