It was claimed by a witness that the 17-year-old victim was chased on to the bus by two males in helmets in Cricklewood, north-west London.
Mail Online has reported that the witness also said one of the attackers was “wielding a long knife”.
Cops and ambulance crews raced to the scene after they were made aware of the stabbing at 5.30pm yesterday.
The teenager was then rushed to a central London hospital by paramedics but his condition remains unknown.
No arrests have been made in connection with the incident yet.
A spokesperson for the Met Police said: “Police were called at approximately 17.30 on Saturday, 27 April to reports of a stabbing on a bus in Cricklewood Lane, near the junction with Cricklewood Broadway, NW2.
“Officers and London Ambulance Service attended and found a male, believed aged 17, suffering stab injuries.
“He has been taken to a central London hospital for treatment — condition awaits.
“Enquiries into the circumstances are ongoing.
“No arrests have been made and a crime scene remains in place at the scene.”
A 21-year-old man was also stabbed to death in a string of four stabbings in just seven hours in London and before that two men in their 20s were rushed to hospital after being stabbed in east London.
Met Police figures show knife crime has increased by 16 per cent in the capital year-on-year in 2018.
In the same year the Met Police also recorded 14,660 knife offences in London -more than any other force in the country.