Passengers on the boat, which had the capacity to carry only about 30 people, were mostly women and children from Ujveria village in Uttar Pradesh.
"As the boat entered the midstream it failed to take the weight of the people and collapsed,'' Shivendra Yadav, a local police official, said
Twenty-five people on board managed to swim to safety and reach the banks of the Ganges, which is revered as a holy river by Hindus.
Rescue efforts have been launched to find the missing passengers.
Boat accidents are common in India, mainly caused by overcrowding, poor maintenance of vessels and a lack of life jackets and other safety equipment.