Rescue efforts are under way across isolated Himalayan regions in India, Nepal and Tibet after a magnitude 6.9 earthquake struck the area on Sunday.
The epicentre was the northern Indian state of Sikkim, where the Indian government says that at least 35 people have been killed.
But the relief effort there has been hampered by rainfall and landslides. It is feared that the toll could rise.
Several earthquakes hit the region this year, but none caused major damage.
'People are panicky'
In Sikkim many buildings are reported to have collapsed while power supplies in many areas have been cut off.
Thick cloud and heavy rain is making it difficult for rescuers.
Indian military helicopters have been unable to take off and aid workers are stranded trying to reach the affected areas. Roads have been destroyed making it difficult to get to mountainous regions.
Officials say that thousands of soldiers helping the relief effort may not reach many areas until Tuesday because the high mountain passes are blocked.
"The situation doesn't look good," an official from the UN's disaster management team in Delhi told the Reuters news agency. "My feeling is the death toll and number of injured are going to increase."
A resident in Gangtok, capital of Sikkim, told the BBC over the telephone that there was panic in the immediate aftermath of the quake and that several buildings were either cracked or tilting to one side. Thousands of people spent the night outside their homes.
A British tourist in the city also spoke to the BBC and said that the quake was so violent that it knocked him over on the third floor of the hotel where he was staying.
It has been raining for four days without respite in parts of Sikkim and shops, businesses and offices in Gangtok are closed. Telephone communications to the affected areas is patchy.
Bhim Dahal, press advisor to Sikkim's chief minister, told the BBC that more than 150 have been injured and the main highway to the north of the state has been blocked.
However officials say that roads connecting the state to the rest of India - through the state of West Bengal - have now re-opened.
Mr Dahal said that the state government building and the police headquarters in Gangtok have been badly damaged and 1,000 houses have collapsed - with 100,000 damaged - across the state.
Tremors were felt in the north-eastern Indian states of Assam, Meghalaya, and Tripura. They were also felt in regions of India: West Bengal, Bihar, Jharkhand, Uttar Pradesh, Rajasthan, Chandigarh and Delhi. Bangladesh and Bhutan also felt the quake.
One person was killed during a stampede as people panicked in a town in the eastern state of Bihar, and other deaths were reported near Darjeeling, in West Bengal.
Latest reports from Nepal say that at least six people have been killed with more than 100 injured. Officials say that significant structural damage has been caused to buildings in the east of the country.
In addition a landslide triggered by the quake has blocked transport along the highway which links the city of Dharan to the town of Dhankuta. Dharan was hit by a devastating quake 28 years ago.
In the capital Kathmandu, three people were killed when a wall at the British embassy collapsed. A budget debate in the country's parliament was suspended for 15 minutes when lawmakers fled the chamber as the entire building shook.
Just over the border in Tibet's Yadong County, just 40km (25 miles) from Sikkim, the earthquake caused hundreds of landslides disrupting traffic, telecommunications, power and water supplies.
Chinese authorities said relief supplies were on the way to the area.