Six people have been arrested following four fatal unrelated stabbings that took place on New Year's Eve and in the early hours of New Year's Day.
In the attacks on New Year's Eve, a 17-year-old boy and two men - aged 18 and 20 - were stabbed.
Later a 20-year-old man was knifed at a house party in Islington, north London.
All four died as a result of their injuries, while a fifth victim, stabbed in the New Year's Day incident, is critically ill in hospital.
Scotland Yard said a 19-year-old man has been arrested on suspicion of murder over the New Year's Day stabbing.
Five males, aged between 17 and 21, have been arrested in connection with the death of the 18-year-old, who was stabbed in Enfield.
Metropolitan Police Commander Neil Jerome called on anyone with information on the attacks to come forward.
"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," he said.
"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."
Sunday's attacks - in Larmans Road, Enfield; Memorial Avenue, West Ham; and Norwood Road near the junction with Station Rise, Tulse Hill - took the total number of people stabbed to death in the capital last year to 80, Scotland Yard confirmed.
The New Year's Day stabbing occurred at a house party in Bartholomew Court, Old Street.