Three people were killed when Sunday's 6.9-magnitude earthquake collapsed a wall at the British mission in Kathmandu, and officials in affected countries warned that the death toll could rise as reports filter in from remote areas.
Tremors were felt more than 1,000 kilometres (600 miles) away in New Delhi to the west, and in Bangladesh to the east.
At least 60 people were injured by mudslides, falling debris and collapsing buildings in Gangtok, the capital of India's Himalayan state of Sikkim.
"There is no electricity. Everybody is out on the road," Gangtok resident CK Dahal told the CNN-IBN television news channel."We all ran out our houses, some even jumped out of their windows. You can see some buildings that have developed cracks," he said.
G Anandan, chief of the central emergency control room in Gangtok, said five people had been killed in the city, and another 10 had died in building collapses and landslides in neighbouring towns and villages.
"There's a good chance the death toll could rise as rescue teams begin to access the more remote areas near the epicentre," Anandan told AFP.
In Nepal, police said a motorcyclist and his eight-year-old daughter were among the three crushed when the wall crumbled at the British embassy compound in the capital Kathmandu, 270 kilometres (170 miles) west of the epicentre.
"Another two died in a separate incident in eastern Nepal," national police spokesman Binod Singh told AFP.A budget debate in Nepal's parliament stopped for 15 minutes while lawmakers leapt to their feet and fled the chamber as the entire building shook.
The quake was felt across a wide region including the Himalayan kingdom of Bhutan after it struck the border of Sikkim and Nepal at about 6:10 pm (1240 GMT) on Sunday, according to the US Geological Survey.
Its epicentre was just over 60 kilometres (40 miles) northwest of Gangtok, at a relatively shallow depth of 19.7 kilometres (12 miles). The quake was followed by two strong aftershocks.
Indian Prime Minister Manmohan Singh called an emergency meeting of the National Disaster Management Authority, and Cabinet Secretary Ajit Seth said air force planes carrying rescue teams and relief supplies had gone to Sikkim.
Telephone landlines to Sikkim, India's least populous state, were knocked out and mobile networks were swamped, making communication with the affected area difficult.
The Press Trust of India said that police rescued 15 foreign tourists in the north of Sikkim, a popular destination for trekkers, but it did not give their nationalities.
Nine other people died in India, including one reportedly killed in a stampede by panicked residents in Bihar state and four who were buried when a house fell down near Darjeeling.
China's official Xinhua news agency said seven people had been killed in southern Tibet, near the border with Sikkim.Strong tremors were felt in Guwahati, the main city in India's Assam state, some 600 kilometres (375 miles) away, sending people running into the streets.
"Our apartment block was literally swaying," said housewife Anamika Das.
In Kathmandu, traffic came to a standstill as hotels and bars were evacuated.Hundreds of anxious tourists and residents waited for news in car parks and on the streets as the seasonal monsoon rain lashed down.
In Bhutan, buildings in the capital Thimphu also shook.India's seven northeastern states, joined to the rest of the country by a narrow sliver of land, are located in an area of frequent seismic activity.
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Condolences.. good luck for the rescue missions.
GOI has made 5 heavy lifter aircraft available for the recue mission.
RIP all those deceased and wishing quick recovery to all those affected in both countries.
RIP for the dead :(
Till this moment 10 people are reportedly killed. Mobile connectivity is down and so is power and it is raining right now...Sikkim and areas around are badly hit. 10 are killed in Nepal too and I am sure soon reports would come from Bhutan. Initial information are few and far between but I guess by tomorrow morning when connectivity would get better. Landslides have happened so roads are blocked too.