Around 40 to 50 people, all from Bitawar district, were on board the boat when the accident took place. While nine people were saved by divers in neighbouring Varanasi, 22 swam to safety in Mirzapur.
Police divers and a team of National Disaster Response Force (NDRF) have also been pressed into service to locate and rescue any survivors, an official told IANS. He, however, said the possibility of any survivors was very little because night had set in.
The Ganga is in spate these days and the water level in the region is rising menacingly every day.
Officials said they feared that the number of missing people could be more.