Incessant monsoon rains have pounded many areas in mostly mountainous Nepal since Thursday, submerging large swathes of land, inundating homes, and destroying bridges and roads across the country.
A Home Ministry statement said 47 people had been confirmed dead and 28 injured. There are 29 missing.
Television channels showed roofs of houses submerged in flood waters in the southern plains and people wading through chest-deep water with their belongings on their heads.
Officials said in some areas rains had eased but some rivers in the eastern part of the country were still above flood level. Authorities asked residents to remain alert.
Nepal police official Ishwari Dahal said all 56 sluice gates of the Kosi barrage on the Nepal-India border had been opened on Saturday night for six hours to drain out 371,000 cusecs of water, the highest accumulation in 15 years. A cusec is a measurement of flow, equivalent to one cubic foot per second.
"Its water level has gone down now," Mr Dahal told Reuters from the barrage site in southeast Nepal.
The Kosi has been a serious concern for both India and Nepal since it broke its banks in 2008 and changed course, submerging swathes of land and affecting more than 2 million people in India's Bihar state. About 500 people died in that disaster.
Rain-triggered floods and mudslides have left a trail of destruction in other parts of South Asia as well. Officials in northeastern India have reported at least a dozen people dead and over a million affected.
The dead included two schoolchildren who were buried when their boarding school collapsed while they were asleep in Tawang in Arunachal Pradesh state.
In Assam state, the State Disaster Response Authority said around 900,000 people spread over 21 of the state's 33 districts have had their homes submerged. Several thousands are living in government-run relief camps.
Elsewhere in Assam, Kaziranga National Park, home to the endangered one-horn rhinoceros, has been flooded. The park is located 225 kilometres (140 miles) east of Gauhati, the state capital.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies