The incident occurred at around 11 am when the bus was on its way to Simdega from Ranchi, the police said.
Khunti sub-divisional officer Pranav Pal said, the mishap took place due to the negligence of the driver.
The driver, Charku Gope, was collecting fare from the passengers leaving the responsibility of driving the bus on someone else, Pal said.
Gope, a resident of Lohardaga district, was among the four killed, the SDO said.
The person who was reportedly driving the bus at that time fled from the spot following the accident, he said.