A 17-year-old boy was attacked with a machete in Scarborough, Ontario, after refusing to let another teen use his cellphone.
The victim tried to run away but was chased by his attacker who continued to slash him from behind, police said.
The victim then ran to a transit bus for help.
Even when a bus stopped to help, the attacker kept slashing away at the teen.
The bus driver activated his emergency button and the machete-wielding suspect at first walked away and then returned to continue the attack.
Police found a suspect hiding under a car nearby.
The victim was taken to hospital in critical condition.
Gajan Ponniah, 19, of Markham, Ont., is charged with attempted murder and robbery.