The bus rolled 150 feet down into the gorge while negotiating a sharp bend at Amraj Ghati in the Garhwa police station area around 5 AM, Garhwa SP Priyadarshi Alok said.
The deceased include the bus driver and a khalasi.
Five seriously injured passengers were referred to the Rajendra Institute of Medical Sciences while 18 others admitted to the Garhwa Sadar hospital, he said.
The bus was heading to Bihar's Sasaram from Chhatisgarh's Raigarh and at least half of the passengers were to get down in Garhwa, five km from the accident spot, according to police sources.