Scotland Yard said police were called at 4.24pm on Sunday to Sandringham Road, Barking, to reports of a stabbing.
The victim, a man in his mid-twenties, is in a critical condition in an east London hospital.
London Ambulance Service and London's Air Ambulance attended the incident, and a crime scene is in place.
Police said two males have been arrested on suspicion of attempted murder.
Meanwhile, a man has been taken to hospital in a life-threatening condition after being stabbed in Hackney, north-east London.
Scotland Yard said officers were called to Brooke Road at about 5pm on Sunday and that no arrests had been made.
At a third stabbing officers saw a fight between two men on the New North Road in Ilford at 5.44pm.
One man in his 30s was suffering a stab and slash wounds. He was taken to hospital where he is also in a life threatening condition.
Another man was arrested on suspicion of grievous bodily harm and remains in police custody.