The bus was en route to Janakpur from Kathmandu and the accident took place at 2 am on the Hetauda-Narayanghat section of the national highway at Jyamire area in the district here, the police said.
The injured passengers are undergoing treatment at the Chitwan Teaching Hospital.
Three of the injured have returned home after receiving medical treatment at the hospital, police added.
The driver and cleaner of the bus fled the spot soon after the accident, police said, adding a search is on to nab them as their negligence is said to be the cause behind the accident.