The male victims - a 17-year-old, an 18-year-old and a 20-year-old on New Year's Eve, and a 20-year-old - all died yesterday due to their injuries, Scotland Yard confirmed.
Sunday's stabbings took place in various locations across London - at 11.30am in Larmans Road, Enfield, 7.35pm at Memorial Avenue in West Ham, and 10.40pm in Norwood Road in Tulse Hill.
A fifth man is in critical condition after the New Year's Day incident which occurred at Bartholomew Court in London's Old Street.
Met Commander Neil Jerome said the incidents were not connected, adding most of the people cooperated with police in London to ensure safe New Year's Eve celebrations.
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"However, there were small groups who chose to engage in disorder and violence, and whose actions have had utterly tragic consequences," said Jerome.
"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," he said.