Witness aboard the bus said Sy started screaming while driving, showing a can of gasoline and a lighter.
One of the students aboard called the police who arrived quickly and stopped the bus near the junction with Peschiera Borromeo, Milan.
Officers broke the rear windows, letting the young students get off the bus while Sy set it alight.
Another student aboard the bus told Repubblica: ‘He was threatening us, saying if we moved he would have poured the gasoline and set a fire.
‘He kept saying that people in Africa die and it is the fault of Di Maio and Salvini.
‘Then the police saved us.’