The accident occurred at Danbaksho of Andharkot village around 9:30pm on Wednesday when the picnickers were on their way to Dinajpur, Chougachha Police Station OC Moshiur Rahman said.
He identified the deceased besides the two girls as Ramkrishnapur High School teacher Juhurul Islam, driver's helper 'Milon', and a shopkeeper. The bodies were kept at the Upazila Health Complex.
The injured could not be identified immediately. They were being treated at several local hospitals.
OC Moshiur said the locals and Fire Service officials recovered the bus from a ditch around 10:30pm.