Floods and landslides unleashed by unrelenting rain in India's eastern hill region of Darjeeling killed at least 18 people, after washing away homes, roads and bridges, authorities said, while the death toll in neighbouring Nepal rose to 50.

Several people were still missing on Monday, as relief and restoration work got underway, said local government officials in India's state of West Bengal, warning that the death toll was likely to rise as details flowed in from remote areas.

"Two iron bridges have collapsed, several roads have been damaged and flooded, huge tracts of land ... have been inundated," Mamata Banerjee, the state's chief minister, said in a post on X.

The districts of Darjeeling, Kalimpong, Jalpaiguri, Alipurduar, which are home to tea plantations, were among those affected, she added.

More showers are expected after the weekend's "extremely heavy" downpours in Darjeeling, said H R Biswas, the regional weather head in the state's capital of Kolkata.

Highway traffic was disrupted as part of an iron bridge over the Balason River linking the city of Siliguri in the plains with the hill town of Mirik collapsed in the heavy rain, and many roads caved in.

Large amounts of debris littered the roads, a local disaster management official said, making it impossible for rescuers to reach many places in the remote area.

The Himalayan hill resort of Darjeeling is famed for its tea and draws tourists with spectacular views of Mount Kanchenjunga, the world's third highest peak. Banerjee urged tourists to stay put until they were safely evacuated.

Across the border in Nepal, the deaths in floods and landslides rose to 50, 37 in separate landslides in the eastern district of Ilam bordering India, a spokesperson for the Armed Police Force said.

Rescuers dug into the mud and debris in the district, hunting for survivors, while also clearing blocked roads after landslides washed away homes in several villages, district official Bholanath Guragain said.