Among the murder victims were two teenagers, including a 17-year-old who may have been killed following an altercation on a bus.
The victims – a 17-year-old, an 18-year-old and two 20-year-olds – died between New Year’s Eve and the early hours on Monday following knife attacks. The four incidents happened in north, east and south London, and none are thought to be linked.
Five males have been arrested in connection with one of the murders, which took place on the morning of New Year’s Eve.
Police said the 17-year-old victim, may have been killed following an “altercation” on a number 68 bus travelling towards Herne Hill.
Sunday’s stabbings – at 11.30am in Larmans Road, Enfield, 7.35pm at Memorial Avenue in West Ham, and 10.40pm in Norwood Road in Tulse Hill – took the number of people stabbed to death in the capital last year to 80.
Of those, 18 involved victims under the age of 19.
The New Year’s Day stabbing occurred at Bartholomew Court, Old Street, in the City.
A fifth man is in a critical condition following another stabbing on the first day of January, Scotland Yard said.
Met Police Commander Neil Jerome said four deaths in such a short period was unusual.
“There were small groups who chose to engage in disorder and violence, and whose actions have had utterly tragic consequences,” he 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.”
The stabbings come at a time when London is already grappling with an increase in crime over the past year. The latest statistics, published in October, revealed that crime across the UK was up by 13 per cent, with a surge in violence in the capital blamed for much of the increase.