While 15 people swam to safety, the remaining 10 others were feared drowned in the river, police said.
Local officials have rushed to the spot to supervise rescue operations, they said, adding divers have been pressed into service.
A National Disaster Response Force (NDRF) team from Patna has been called in to assist rescue and search operations.
The occupants of the boat were on way to Karwa bazar from Anuwa village.
