The flood surged through the Bhote Koshi River at around 9 am (local time) coming from the Tibet side affecting Rasuwa and Dhading districts bordering Tibet and Nuwakot district, southwest of Kathmandu, officials said.

The flooding was not caused by local rains in Rasuwa but possibly because of the heavy rainfall or avalanche on the Tibetan side, they said, but the exact cause is yet to be ascertained.

Multiple downstream districts, including Rasuwa, Nuwakot, Dhading and Chitawan, have been placed on high alert even as officials started search and rescue operations with the help of Nepal Army in the affected areas.

The sudden rise in water caused widespread destruction in Timure in Rasuwa district and the nearby Syafrubesi area, with vehicles, goods and other property washed away, the Nepal Army said in a statement.

The most affected is Rasuwa, about 125 kms northeast of Kathmandu, situated near the Tibet border. The bodies of three men and a woman were recovered from Bidur Municipality of Nuwakot district after the flash flood, Senior Superintendent of Police and spokesperson at Bagmati Province Police Office told PTI.

Their bodies were found lying near the Trishuli river soon after the flood, he said.

The National Disaster Risk Reduction and Management Authority (NDRRM) of Nepal, in a statement, called people residing near river banks of Rasuwa, Nuwakot, Dhading, Chitawan and Gorkha to remain on high alert and take safety measures until further notice.

According to the Department of Hydrology and Meteorology, Wednesday’s flooding was not caused by rainfall in Rasuwa. The flooding did not appear to have been caused by heavy rainfall in Rasuwa itself, according to Dinkar Kayastha, information officer at the Department of Hydrology and Meteorology.

It might have been caused by either formation of a new glacier or bursting of the old one, he added. “We are still studying the matter, so the real cause is not yet known,” he said and maintained that the risk of the flood from the Tibetan side has not yet vanished, so “we need to be cautious.”

Investigations are under way to determine the cause of the sudden surge, with officials examining whether it was triggered by a glacial lake outburst flood (GLOF) or another factor, The Himalayan Times said.

Rasuwa Assistant Chief District Officer Dhruva Prasad Adhikari said the scale of the flooding was unusually large and that the two settlements had suffered significant damage.

Rasuwa Chief Customs Officer Rajendra Dhungana said numerous vehicles and goods kept at the customs premises were swept away. A recently constructed bridge was also destroyed. This is a place which regulates Nepal's trade traffic connecting Tibet, China.

The flash flood damaged in-operation eight hydropower projects with a total capacity of 354 MW and five under construction projects located in Nuwakot and Rasuwa districts, according to a statement by Independent Power Producers' Association Nepal (IPPAN).

The major in-operation hydropower projects damaged by the floods include Rasuwagadhi Hydropower Project (111 MW), Sanjen Khola Hydropower Project (78 MW) and Upper Trishuli 3A (60 MW).

The Kathmandu Post quoted Chameli Gurung, deputy chair of Uttargaya Rural Municipality, who said around a dozen settlements, including Syaphrubesi, Betrawati, Mailung, Salletar, Shantibazar, Pairebesi, Khalti Basti, Sole, Trishuli and Battar, had been affected.