Police came across a fight in progress between two men on New North Road in Ilford at 5.44pm on Sunday, 16 February.
London Ambulance Service also attended and a man in his 30s was suffering a stab and slash wounds.
He was taken to hospital where he is in a life-threatening condition.
A man (no further details) has been arrested on suspicion of GBH. He remains in police custody.
A crime scene is in place