Police say a 15-year-old boy had been arrested on suspicion of grievous bodily harm after the attack in Tower Hamlets.
Officers were called at 3.30am on Sunday by paramedics after reports of a stabbing on Upper North Street, a five minute walk north of Canary Wharf station.
They found the teenage boy, whose exact age is not known, with a stab injury to his chest.
He was rushed to hospital where he remains in a critical condition.
A spokesman for the Met Police said: "Police were called by London Ambulance Service at 3.30am on Sunday to Upper North Street following reports of a stabbing.
"Officers attended and found a teenage boy suffering from a stab injury to his chest.
"He has been taken to an east London hospital, where his condition is being treated as life-threatening.
"A 15-year-old boy has been arrested on suspicion of GBH and taken into custody.
"Officers remain at the scene and enquiries into the circumstances continue."
Anyone who has information that could assist police should call 101 ref CAD 1150/12 January.
