Rain and landslides have hampered the search for survivors of a 6.8 magnitude earthquake that killed at least 39 people in isolated Himalayan regions stretching across India, Nepal and Tibet.
Thick cloud kept helicopters from flying over the affected areas and authorities say the number of casualties could rise as rescue teams have not been able to reach remote areas.
18 casualties were confirmed in the northeastern state of Sikkim, the epicentre of last night's quake, with more deaths reported in neighbouring Nepal and Tibet.
"The situation doesn't look good." an official from a UN disaster management team in New Delhi said.
"My feeling is the death toll and number of injured is going to increase further."
Sikkim, the country's most sparsely populated state located in the Himalayas surrounded by Nepal, Bhutan and Tibet, is prone to landslides, with the number of high-rise buildings rising in its mountain towns due to India's economic boom.
At least two died in Bihar state, south of Sikkim, while five died in the Indian state of West Bengal.
"Even if the number of casualties is low, there is likely to be a huge need for humanitarian assistance for affected civilians whose homes have been destroyed and who need food and shelter. The UN is taking this very seriously," said the UN official, who declined to be identified.
Outside India, at least seven people died in neighbouring Nepal, three of them killed when a wall on the perimeter of the British embassy in Kathmandu collapsed onto a car and a motorcycle. Seven were also reported dead in China's restive Tibet region, China's state-run news agency Xinhua said.
Landslides and heavy rain were slowing the arrival by road of at least 400 rescue workers and doctors trying to reach the worst affected area after landing at the nearest airport almost 100km away.
Many towns in Sikkim experienced power cuts, while thousands are being sheltered by the government.
At least 100 people were injured in Sikkim alone, while hundreds of tourists, mainly Indian, were stranded on the main road out of the state to West Bengal in the south.
The quake was felt all the way to New Delhi in India and Bangladesh.
