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At least 15 others were injured in the crash reported from the district's Gobindaganj Upazila, said local highway police station OC Md Abul Bashar.
He said the accident happened around 3am on Sunday near Jummaghar's 41 mile area on the Dhaka-Rangpur Highway.
A truck carrying stone rammed into a bus heading for Sayedpur, throwing it into a roadside ditch.
Four passengers, including a child, died on the spot, said OC Bashar.
One injured victim died at the Gobindaganj Upazila Health Complex in the morning. The death toll may yet rise, doctors said.
The identity of the victims is yet to be ascertained.