Three teenagers were found stabbed within minutes of each other in northeast London.
The first victim, a boy believed to be 15-years-old, was found with a stab wound in Waltham Forest on Monday afternoon.
Within minutes police were called to a nearby address where two 19-year-old men were also found with stab wounds.
All three victims were taken to hospital where their condition is not yet known.
Four arrests have been made, Scotland Yard said.
The stabbing follows a spate of knife attacks across the capital.
Last week a man appeared in court in connection with five knife attacks that took place in Edmonton, north London.
One of the victims, a 45-year-old woman, was left paralysed after her spinal cord was severed in the attack.
In Waltham Forest 14-year-old Jaden Moodie was stabbed to death earlier this year after a group of five men in a black Mercedes rammed him off a moped, police believe.
Anyone with information is asked to call police on 101 or Crimestoppers anonymously on 0800 555 111.
