More than 35 houses and bridges were swept and a hydropower project was damaged in a flash flood in Nepal's Gorkha on Sunday, months after thousands were killed in a similar disaster in the Himalayan country.

The flash flood occurred in the Chumnubri village in Gorkha district after the water level increased in Budhi Gandaki, a tributary of the Trishuli River, downstream from another tributary where a glacier collapse caused a flood on August 26, killing 1,457 people and leaving thousands missing.

Videos posted on social media showed the river turning completely black and grey and flowing with thick mud and debris.

The water level increased from 3.66 metres at 6:30 AM to 8.43 metres at 8:40 AM, well above the danger mark of 5 metres, Nepal's National Disaster Risk Reduction and Management Authority (NDRRMA) said.

The water level increased by over two metres within 10 minutes between 8:30 AM and 8:40 AM, it said.

"Since the flood also washed away the measurement centre, including the bridge, further details could not be obtained," the NDRRMA said in a press release at 11:50 am.

The agency also said that the flood was not caused by rain.

"Based on preliminary information and observation of satellite images, it is estimated that the river may have been blocked and then breached, causing a sudden flood. Detailed technical analysis of the actual cause of the incident is ongoing," it said.

No casualties have been reported so far, an officer said.

Residents of the coastal and lower coastal areas of the river have been requested to stay in a safe place and away from the river bank and at-risk settlements till Sunday evening.

Nepal Army has been deployed by air and land to carry out search and rescue operations.

The teams conducted aerial reconnaissance and ground assessments of the affected areas and airlifted six people to safety from Jagat, an area at risk from landslides, the army said in a statement.

"A Composite Quick Reaction Team stationed in Kathmandu was also airlifted to the affected area," it said.

Nepal is still reeling from August's devastating flash floods originating near the Nepal-Tibet border.

The Bhotekoshi River, which flows south from the Himalayan border region, carried the floodwaters downstream, sweeping away homes, vehicles, roads and bridges and damaging hydropower projects.

Sun News/ rabbi