The incident occurred Friday morning in the town of Puente de Ixtla in southwest Morelos and some 30 kilometers from the prison.
The Morelos government confirmed in a statement the death of four employees and said four others were being treated for injuries at a local hospital.
The state government asked for immediate intervention of the federal government to help curb local criminal organizations.
“The local government stands firm in its commitment to protect families and not make deals with criminals at any time,” said the statement.
According to local media, the attack was carried out by three armed men who fired shots at the bus and then fled in a car.
It has been the second violent attack this week in Morelos. On Wednesday, a man shot and killed two local union leaders in the main plaza of the city of Cuernavaca, the state’s capital.
