Floods and landslides triggered by days of torrential rain have have killed at least 99 people in Nepal since Monday, officials said.

In neighbouring India, heavy downpours this week have also caused havoc, killing at least 88 people, while flooding roads, destroying bridges and causing landslides that washed away several homes.

Police in Nepal said rescuers were looking for at least 40 people who have been reported missing, sparking fears that the death toll could rise.

A majority of the deaths occurred in the country's eastern and western regions, which saw heavy rain this week, said police spokesperson Basanta Bahadur Kunwar.

"The search and rescue team have been relocating people to safer locations and taking the injured to the hospitals," he said.

At least 35 injured in the storms have been rescued and are in hospital.

"Crops and homes have been wiped out, which is a severe blow to families already grappling with the devastating fallout of the Covid-19 pandemic," said Azmat Ulla, of the International Federation of Red Crescent Societies in Nepal.

Red Cross teams are aiding evacuation efforts in both countries.

"The people of Nepal and India are sandwiched between the pandemic and worsening climate disasters, heavily impacting millions of lives and livelihoods," he added.

On Thursday, Prime Minister Sher Bahadur Deuba visited the flood-affected areas in the western region and directed authorities to focus on the speedy rescue, relief and rehabilitation of those vulnerable.

Authorities are still trying to ascertain the number of displaced households and the full extent of the damage caused by the disasters.

India has seen large amounts of rain across several regions this week.

Flooding and landslides caused by downpours over the week have killed at least 46 people in the northern state of Uttarakhand and 42 people in the southern state of Kerala, which is on alert for more rain in the coming days.

Landslides and floods are common in India's Himalayan north. Scientists say they are becoming more frequent as global warming contributes to the melting of glaciers in the area.

In February, flash floods killed nearly 200 people and washed away houses in Uttarakhand. In 2013, thousands of people were killed in floods in the area.