At least a dozen people have been killed in Bhutan and Nepal and several others are missing as torrential monsoon rains hit the region, triggering landslides and inundating homes, officials said Thursday.

The annual monsoon season is crucial to replenish water supplies across South Asia, but it also causes death and destruction.

Ten collectors of cordyceps -- a fungus valued for its alleged aphrodisiac properties -- died when their remote mountain camp north of Bhutan's capital Thimpu was washed away early Wednesday.

Five others were injured and were in a stable condition in hospital, officials said.

Bhutan's Prime Minister Lotay Tshering offered his prayers and condolences and said a rescue team had been sent to the site.

"I urge everyone across the country to avoid visiting or camping by the riverside, and to be cautious of such possible mishaps during (the) monsoon," he added in a message on Facebook.

In Nepal, the bodies of two Chinese workers were recovered on Thursday from Sindhupalchok near the capital Kathmandu, taking the total death toll from floods in the district to three.

Their bodies were found more than a hundred kilometres from where they had initially been swept away by the overflowed Melamchi River, officials said.

Thirteen others are still missing while hundreds more were displaced from their homes, they added.

"We still see possibilities of rescuing alive those who are missing, because some of them could be taking shelter in safer places," Arun Pokharel, the local district chief, told AFP.

More than 70 people have been rescued so far. 

But rescue efforts have been hampered by telecommunication failures in the area, Pokharel added.

The number of deadly floods and landslides has increased in recent years in Nepal. Experts say climate change and more road construction could be triggering the deadly disasters.

More than 200 people were killed in landslides and floods during last year's monsoon season in Nepal.