Eight Indian tourists, including four children, have been found dead in their room at a hill resort in Nepal on Tuesday, police said.

The eight - two couples and their four children - had slept in one room at a hotel in Daman, a popular tourist destination in Makwanpur district about 55 kilometres (34 miles) from Kathmandu known for its panoramic views of the Himalayas.

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"They were found unconscious this morning and airlifted to Kathmandu but died during treatment," police spokesman Shailesh Thapa Chettri told AFP news agency.

Deeply distressed by the tragic news of the passing away of 8 Indian tourists in Nepal.Our Embassy @IndiaInNepal hs been closely following the situation.Embassy officials are stationed at the hospital& are providing necessary assistance.Our thoughts are with the bereaved families — Dr. S. Jaishankar (@DrSJaishankar) January 21, 2020

"We suspect they died of suffocation, but autopsy reports will confirm the cause," Chettri added.

The families used a gas heater in their room to keep warm, a district official told AFP. They were part of a group of 15 who had travelled to Nepal from the southern Indian state of Kerala.

A doctor at the Hospital for Advanced Medicine and Surgery in Kathmandu, Kamal Thapa, said the eight people showed no signs of life when they arrived at the hospital.

Tourism is a major source of revenue for Nepal's economy, providing hundreds of thousands of jobs. Last year just over 1 million tourists visited the country, of which the biggest contingent - around a tenth - came from India.