"Officers believe they know the identity of the deceased and next of kin have been informed".
A crime scene is in place, and West Ham Lane has been closed between Widdin Street and Paul Street.
The boy, who has not yet been named has been taken to a north London hospital, was treated for non-life threatening injuries.
The latest killing involves a 42-year-old man who was discovered collapsed and suffering stab wounds in Whalebone Lane, near West Ham Lane, in Stratford on Monday morning. The victim was pronounced dead 20 minutes later.
Just 12 minutes later, Construction student Cheyon Evans, 18, was stabbed to death in Tooting, south west London, at 4.42pm.
Witnesses said he was stabbed repeatedly by a gang of teenagers.
Four teenagers who were arrested on suspicion of murder on Friday were later bailed pending further inquiries.
The murders of at least four people in as many days have triggered a massive investigation by London police and an increase of patrols across the British capital in a bid to stem the eruption of violence.
A 17-year-old from Merton, who can not be named for legal reasons, and Mohammed Nadir Dafallah, 18, from Wandsworth, have been charged with murder and were due in court on Monday.
Officers were ambushed by around 100 youths and were pelted with bottles, while polcie seized a large hunting knife found on the floor.
On Saturday, U.S. President Donald Trump slammed London mayor Sadiq Khan's record as the capital's bloodbath continued.
A City Hall spokesman said Mr Khan was focusing on supporting communities and he was "not going to waste his time" responding to the president's tweet.
Khan retorted by saying Trump is seen as "a poster boy for racists around the world".
Police and paramedics rushed to the area and established a crime scene.
The incidnets five separate attacks all over London in the space of 24 hours that left three men dead and three others injured. It was also sunny at the time and a number of people would have been enjoying the weather in the area of Plumstead Gardens; I need you to come forward.
"You can't sugar-coat that the last four days have been bad", he said.