The condition of 12 passengers was serious. Of the five persons who were killed, two were minors, the police said.
Rajauli Police Station Officer-in-charge Awadhesh Kumar said the driver had lost control over the vehicle. He may have dozed off at the wheel, he added.
The accident occurred around 2 am on NH 31 near Andharbari village when the bus was on its way to Biharsharif, the district headquarter town of Nalanda, from Kolkata, the police officer said.
All the victims were residents of Budhaul Beldariya village under Town Police Station of Nawada district. The identity of the deceased, however, has not been ascertained so far, he said.
The twelve passengers, who sustained serious injuries, have been referred to Patna Medical College and Hospital.
The rest of the injured have been admitted to Rajauli sub-divisional hospital and Nawada Sadar hospital, he said.