Scotland Yard confirmed the male victims – a 17-year-old, 18-year-old and a 20-year-old on New Year’s Eve, and a 20-year-old in the early hours of Monday – all died as a result of their injuries.
Five men have been arrested in connection with one of the deaths, the Metropolitan Police said.
Police condemned the “senseless violence” and the “small groups who chose to engage in disorder and violence” on New Year’s Day.
The second, at around 7.30pm last night, was a fatal stabbing of a 20-year-old man in West Ham.
Then a 17-year-old man was stabbed to death in Tulse Hill.
And at around 2.35am on 1 January, a 20-year-old was fatally stabbed in Old Street. A second male, in his 20s, was taken to hospital with critical injuries.
A schoolboy was stabbed to death in Tulse Hill
“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 urged anyone with any information to call police on 101 or Crimestoppers on 0800 555 111.
Four have died in a spate of unrelated stabbings across the city
The latest deaths will be seen as a setback to London mayor Sadiq Khan and his aim to get a stranglehold on the year-on-year increase in knife crime in the capital, which has seen the launch of a high-profile “London needs you alive” campaign and knife crime strategy.
At his last Mayor’s Question Time, Mr Khan said: “Every death on the streets of London is an utter tragedy and I’m deeply concerned about the rise in knife crime.