At least eight people were killed and nearly 100 injured Sunday as a 6.8 intensity earthquake violently hit the Sikkim-Nepal border region, jolting large parts of India, Bangladesh and Nepal too.

Tens of thousands scurried out of their homes just after 6 p.m. in numerous cities including New Delhi following the powerful tremor that was quickly followed by two major aftershocks.

The India Meteorological Department (IMD) said the epicentre of the quake was on the Sikkim-Nepal border.

Prime Minister Manmohan Singh immediately convened a meeting of the National Disaster Management Authority.

In no time, the Indian Air Force flew five cargo planes with relief material and rescue personnel for deployment in West Bengal and Sikkim, which accounted for three deaths.

One of the dead was a child, officials in Gangtok said. Another was Sandipan Banerjee, an official with a pharmaceutical company who died when a house collapsed in Rangpo, 40 km from Gangtok.

Another man died when his vehicle was trapped in a massive mudslide on the outskirts of Gangtok.

The worst, officials said, was feared in the Sikkim-Nepal border region, where mudslides had blockaded roads.

At least five people were killed in Nepal, three of them in Kathmandu alone, triggering panic and chaos all across the Himalayan kingdom, news reports said.

The British embassy in Kathmandu, located in the Lainchaur area close to the Indian embassy, collapsed after the quake, smashing a car and killing three people inside.

Dozens were injured as houses crashed across the mountainous country, snapping communication lines.

Across India, buildings shook triggering panic almost all over northern and eastern India, including Delhi, Uttar Pradesh, Uttarakhand, Jharkhand, Bihar, West Bengal, Assam and Mizoram.

In Assam's major city Guwahati, people ran out of their homes.

Power supply was disrupted in parts of northern West Bengal, Chief Minister Mamata Banerjee said in Kolkata.

"In no time all the people in my neighbourhood were out of their apartments," said Anjani Kumari, who lives on Boring Road in Patna, Bihar.

The experience was particularly frightening for those in high rises.

"I was watching TV and for a few seconds thought my head was spinning. When I realised it was an earthquake, I ran out," said Meenakshi Sinha, who lives on the seventh floor of an apartment complex in Noida.

She said the tremors lasted 30 to 40 seconds.

Lucknow resident Vijay Dutt told IANS: "There were strong tremors. In our building, everybody rushed out fearing the worst. The furniture shook and windows rattled. It was scary," he added.

In Tripura, officials said the quake was also felt in neighbouring Bangladesh.

This is the fourth earthquake to hit India this month.

An earthquake measuring 4.2 on the Richter Scale had shaken north India Sep 7 at around with its epicentre near Sonepat in Haryana, 65 km from New Delhi.