Ten people are still missing, while 20 have been rescued, Indian authorities said.
The boat was carrying students to school when it capsized. A team from the National Disaster Response Force (NDRF) is leading the rescue operation.
NDRF Deputy Commandant Randhir Singh said that the NDRF control room received information about the boat capsize around 11am. A team of divers has been deployed to search for the missing people.
Chief Minister Nitish Kumar has directed senior officers, including the District Magistrate, to the scene of the accident. He has also said that the state government will provide all assistance to the affected families.
The cause of the boat capsize is not yet known. (ILKHA)