At least 50 people, including 23 in Sikkim, have been killed in the powerful earthquake that triggered widespread landslides and road blockages making rescue work on Monday more difficult in the worst-hit Himalayan state.

Another eight people, who were travelling in a bus of Teesta Urja Limited, are presumed dead as their vehicle got stuck under the debri of a landslide caused by the 6.8 magnitude tremblor last evening, Major General S.L. Narasimhan, GOC 17 Mountain Division, told reporters here.

The overnight toll climbed to 50, with 23 people being killed in Sikkim, six in West Bengal, seven each in Bihar, Nepal and Tibet, official reports said.

Over a hundred people have been injured in the quake which has left a trail of devastation in Sikkim, causing hindrances in relief work because of landslides and road blockades, they said.

Narasimhan said army has launched ‘Operation Madad’ in Gangtok and other areas by deploying over 2,500 troops.

"Around 44 columns of army are working in various parts of Sikkim, while another 15 are in the East District of the state. We are also sending teams to Darjeeling and Kalimpong (in West Bengal)," he said.

Two districts — West and South — in Sikkim remained inaccessible to the Army, delaying rescue work, he said, adding that the local authorities were carrying out relief work and army commanders stationed there have been alerted.

The casualties have occurred mostly in the north district and in towns and villages like Rangpo, Dikchu, Singtam and Chungthang located along the course of Teesta river, officials said.

A group of 14 tourists were rescued by the army from north Sikkim last night, Narasimhan said.

In Delhi, Prime Minister Manmohan Singh announced Rs 2 lakh as ex-gratia to next of kin of those killed in the earthquake and Rs 1 lakh each for those seriously injured.

Around 300 rescue workers from the National Disaster Response Force were stuck at Bagdogra Airport as chopper services to Gangtok have been suspended due to inclement weather, officials said.

Sikkim chief minister Pawan Chamling announced an ex-gratia compensation of Rs 5 lakh for the kins of the deceased, Rs 50,000 for those grievously injured and Rs 25,000 for those with minor injuries.

Union home secretary R.K. Singh said in Delhi that road communication in Sikkim, disrupted due to landslides affecting rescue and relief operations, was likely to be restored by tonight as Border Roads Organisation personnel were working round the clock to remove the blockades.

"We will restore the road communication by tonight. The situation is under control and army, ITBP and SSB personnel already deployed in Sikkim are helping in rescue operations," he told reporters here.

In Kolkata, West Bengal chief minister Mamata Banerjee said that the quake had left six people dead in different areas in north Bengal. She said she will be going to Kurseong in Darjeeling district to get a first-hand account of the situation.

"I have already sent industry minister Partha Chatterjee and North Bengal affairs minister Gautam Deb to Kurseong. The district magistrate and superintendent of police of Darjeeling are also there. After assessing the situation, we will decide the next course of action," she said.

Banerjee said while helicopters have been kept ready for movement of health and disaster management personnel, they have not been able to proceed to Sikkim due to bad weather.

She said efforts were on to repair the damages to NH-31A and NH-55 caused by landslides on a war-footing. She also announced compensation of Rs 2 lakh each for the next of kin of those who died in the state.

With reports of five more quake-related deaths, the tollin Bihar mounted to seven with reports of damages to property being received from the affected areas.

While Darbhanga alone accounted for four deaths, one person each died in Nawada, Nalanda and Bhagalpur districts, official reports reaching the state headquarters said.

Chinese state-run news agency Xinhua reported that at least seven persons have been killed and 22 others injured in Tibet in the quake which has caused landslides and has disrupted traffic, power and water supplies as well as telecommunication in Yadong County, an area 40 km away from Sikkim.

Three people were killed at Lainchaur in Kathmandu, two in Sunsari district, and one each in Dhankuta and Sankhuwasabha districts in eastern Nepal, according to Home Ministry sources in the Nepalese capital.

In Gangtok, power was restored this morning. Residents had spent the night outside their houses fearing aftershocks. At least 20 aftershocks throughout the night had created panic in the city. The toll in Sikkim till last night was seven.

Many buildings in and around Gangtok have collapsed and around 85 per cent of structures and houses have developed cracks due to the quake that hit Sikkim and other areas last evening, they said.

Most of the areas in north Sikkim have been cut-off from the rest of the country as roads were blocked and communication lines got snapped. All BSNL telephone landlines in the city have gone dead since last evening.The Sadar police station in Gangtok was badly damaged due to the tremor.

The epicentre of the quake — the biggest in two decades — was located at Mangan and Sakyong areas, over 50 km from Gangtok on the Sikkim-Nepal border.

Tremors were also felt in Assam, Meghalaya, Tripura, Jharkhand, Uttar Pradesh, Rajasthan, Chandigarh and Delhi.