KATHMANDU (AFP) - Helicopters ferried people to higher ground in flood-devastated western Nepal after rains left at least 31 people dead, 63 missing and displaced tens of thousands, officials and media said.

The government ordered local officials to accelerate rescue operations after the rains triggered massive landslides in the mountainous regions and flooding on the plains of west Nepal.

At least 31 people were killed and more than 60 are missing after landslides and floods across Nepal brought on by torrential monsoon rains. [AFP]

Army helicopters flying rescue missions carried stranded people away from fast-flowing floodwaters to safer areas, state-run television showed.

Government spokesman Baman Prasad Neupane said Home Minister Krishna Prasad Sitaula, who made an aerial tour of the area Monday, had "directed the local administration in the flood- and landslide-affected areas to speed up rescue efforts".

He said rescuers were urgently trying to discover the fate of 63 people in a village in badly-hit Banke area in mid-western Nepal that has been cut off by floods.

He said the village inhabitants were missing but could not confirm the overall death tally of 31 reported in the media.

Monsoon rains that sweep Nepal and the rest of the subcontinent in the summer cause hundreds of deaths every year from flooding and landslides.

The worst flooding this year has been in Banke district, 510 kilometres (318 miles) west of Kathmandu, where 377 millimetres (15 inches of rain) fell over the weekend, local meteorological officials said on Tuesday.

The Rapti River flowing through the district broke its banks, washing away scores of mud houses and forcing tens of thousands of people to flee to higher ground.

"Some 40,000 people were displaced by the floods ... due to the incessant rainfall," said Banke chief district officer Narendra Raj Sharma.

One journalist in Banke, Janak Nepal, quoted locals as saying the flooding was the worst in four decades.

Officials said that the waters were gradually receding as the rains stopped and India opened a dam bordering Nepal.

"The water level has fallen after the Indian administration ...agreed to open the Laxmanpur Dam that was holding back floodwaters," Sharma said.

State-run television said nine labourers working on a road construction site died when they were hit by a landslide late Monday in the remote northern Mustang region.

Another 22 were killed in floods and landslides over the last two days, the Kathmandu Post reported.

The government has released an initial 28,000 dollars in relief for badly hit areas, the media said, and more funds were expected later.