The death toll from Sunday's strong earthquake in Sikkim, India, has now reached 40 and more than 100 are injured, Times of India reported.

The 6.8 magnitude earthquake also caused buildings to collapse, power outages in several cities and provinces, and triggered powerful landslides blocking off several roads to Sikkim's capital city, Gangtok.

India's Union Home Ministry said 16 landslides in 10-kilometer stretch slowed the rescue operation. News reports said 400 personnel from National Disaster Response Force were struggling on foot to clear the blockade.

The Indian Air Force dispatched two C-130J aircraft carrying relief materials to 200 National Disaster Relief Force personnel, and an IL-76 plane deployed to Bagdogra carried eight tons of relief materials and 110 passengers, a related report said. At least 72 columns, combat engineers, infantry troops, five cheetah helicopters and four Dhruv were also deployed by the army.

The relief effort also includes a 20-man medical team, two AN-32 medium lift aircraft, and eight helicopters, AP reported.

As of Monday, 20 strong aftershocks have been felt, sending residents including tourists in panic and preventing them from going back to their houses. Authorities fear there might still be hundreds of tourists trapped in Gangtok, a tourist spot and capital of Sikkim.

Meanwhile, in Kalimpong area in West Bengal, the casualties have reached five. Chief Minister Mamata Banerjee is set to visit the worst-hit areas.