Police said the attacker, who was caught at the scene, was in dispute with a hospital where the boy’s father worked as a cashier.
Video footage from cameras on the bus showed the 54-year-old man, surnamed He, following the boy onto the bus around 6:20am on Monday and sitting in the row in front of him before launching his attack.
The driver heard the boy’s shouts and stopped the bus, holding the attacker back with one hand as he tried to protect the defenseless victim.
The boy managed to walk from the bus but was bleeding badly. He received emergency treatment in hospital and is now out of danger.
Five other passengers — an elderly man, two schoolgirls and two women — appeared to do nothing to help, according to video.
Police were quickly on the scene and apprehended the attacker.
They said He had been treated at Yuejiaqiao Township Hospital for emphysema, later being transferred to other hospitals. But the transfers caused insurance complications when it came to settling the bill.
During one visit to the township hospital about the problem, police said, He caused a disturbance but was stopped by the cashier, surnamed Kong, the boy’s father. The boy’s mother also worked at the hospital.
According to the Legal Evening News, He blamed the hospital for his insurance problems. He is also said to have accused Kong of hitting him during the disturbance, for which he was demanding an apology and compensation.