Rescue workers are continuing to battle damaged roads and landslides in an effort to reach areas struck by Sunday's Himalayan earthquake that killed at least 100 people.

The 6.9-magnitude quake was centered in the Indian state of Sikkim but caused damage and fatalities across northeastern India, Nepal and the Chinese region of Tibet.

Authorities say the quake triggered a landslide which buried at least 40 workers from a hydroelectric power plant in the town of Saffo in north Sikkim state. At least 12 workers were killed instantly, and more remain missing.

Many of the victims in Bihar and West Bengal states were killed by the collapse of buildings that had already been weakened by heavy monsoon rains.

Nepalese authorities reported eight quake-related deaths, while China's official Xinhua news agency said at least seven people were killed in southern Tibet.

Multiple landslides, fog and heavy rain had prevented many rescue workers from reaching the impact zone. Rescue efforts were in full effect Wednesday after more than 5,000 army troops also blasted though rockfalls to clear a major highway leading to Mangan, a town near the epicenter.

India's Home Secretary R.K. Singh said Tuesday that helicopters were being used to survey the damage and warned the death toll could increase.