A strong earthquake has shaken northeastern India and Nepal, killing at least 23 people, damaging buildings and sending politicians in Kathmandu, Nepal's capital, running into the streets.
The quake, with a preliminary magnitude of 6.8, was felt on Sunday night across north India, in the cities of Guwahati, Kolkata and the capital of New Delhi.
It triggered at least two aftershocks of magnitude 6.1 and 5.3, said RS Dattatreyan, an Indian seismology official, who also warned more aftershocks were possible.
Nepal's government said five people died and dozens were hurt there, including three caught in a wall collapse at the British embassy, 270km west of the quake's epicentre.
In India's Sikkim state - which borders Nepal, Bhutan and Tibet - at least five people were killed and dozens injured in and around the capital, Gangtok, Chief Secretary Karma Gyatso said.
The epicentre was located around the Mangan and Sakyong areas, some 50km from Gangtok on the Sikkim-Nepal border.
At least six people died in other parts of 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.
The full extent of damage was not immediately known because the region is sparsely populated, with many living in remote areas which were cut off by mudslides triggered by the quake.
"There is no electricity. Everybody is out on the road," CK Dahal, a Gangtok resident, told the CNN-IBN 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.
TV stations reported buildings collapsed across Gangtok, 68km southeast of the earhquake's epicentre.
The Indo-Tibetan Border Police said two of its buildings had collapsed in Gangtok.
"We have sounded a high alert. Police are on the streets in Gangtok and other major towns," Jasbir Singh, the state police chief, said.
Singh said rescuers were working overnight to search for anyone pinned under fallen buildings in the city, which has a population of 50,000.
The Press Trust of India news agency said that police rescued 15 foreign tourists in the north of Sikkim, a popular destination for trekkers, but it did not give their nationalities.
Electricity and some phone services were interrupted in the area and power lines snapped in the West Bengal cities of Darjeeling and Kalimpong, which "are now in total darkness", Bengal Chief Minister Mamata Banerjee said.
As many as 1,000 prisoners at Jalpaiguri prison in West Bengal state were escorted from their cells under guard after the building was damaged by the quake, officials reported.
Prime Minister Manmohan Singh offered to send troops to help, and summoned the National Disaster Management Authority for an emergency meeting.
The air force sent five planes to help with rescue efforts.
'Books fell from shelf'
In neighbouring Nepal and Bangladesh, the earthquake sent residents rushing out of their homes, offices and shopping centres.
In Kathmandu, members of parliament who were debating the national budget ran out of the assembly hall into a parking area. They returned 15 minutes later and resumed their session, but 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 were also rocked.
"Our wooden house is safe. Jars fell in kitchen, books fell from shelf," Thimphu resident Aby Tharakan, a media consultant, said in a message posted on the microblogging website Twitter.