The accident occurred in the Dhabanya area of Morang district along the East-West Highway.
The accident happened when a bus heading towards Dharan from Kakadvitta overturned after the bus driver lost control of the bus due to over speed, police said.
The injured are admitted at BP Koirala Institute of Health Sciences, they added.
Road accidents are on rise in Nepal. 62 people have died in five separate accidents in the last one month.
Bad roads, driver's negligence, over speed and overloading were the main reasons behind these accidents, police said.