The incident occurred at about 6 PM at Siddhnath Ghat in Jajmau where 12 persons of Shivkatra colony in Lalbangla area were on a boat which lost balance and capsized, District Magistrate Kaushal Raj Sharma said.
Three persons, including a woman, were rescued by the locals and they have been sent to a hospital where two are in serious condition, he said.
The DM said nine others are still missing and four women and as many children were a part of the group on the boat.
He said a steamer has been pressed in service and a net is being placed in the water. He also said ambulances and a team of doctors have been called to the site.
Senior districts officials including SSP Shalabh Mathur, ADM Avinash Singh are present at the site to supervise the search operation.