Gangtok: At least 20 people were killed after an under-construction tunnel for a hydroelectric project collapsed in Sikkim's Namchi district. Five people, including 43-year-old Aneesh Mohan from Koorothuparambil in Pampady, Kottayam, remain missing following the incident. Rescue operations have been intensified to reach those trapped inside the tunnel.

Aneesh is the manager of the Sikkim unit of the National Hydroelectric Power Corporation (NHPC), a central government-owned enterprise. Aneesh's wife, Sangeetha, has left for Sikkim.

Aneesh has been working with NHPC since 2011 and is based in Delhi. The tunnel, being constructed by NHPC for the Teesta Hydroelectric Project at Samardung in South Sikkim, collapsed at around 1 pm on Monday. The massive tunnel is designed to channel water from the dam to the power generation facility through the mountains.

According to NHPC, the collapse was triggered by an explosion caused by a methane gas leak while rock excavation work was underway underground. At the time of the accident, 25 people, including Aneesh, other officials and workers, were inside the tunnel.

A specialised rescue team from West Bengal, experienced in mine rescue operations, has joined the search efforts. The Sikkim government has constituted an expert committee to determine the cause of the methane gas leak.

The state government has announced an ex gratia of ₹4 lakh for the families of those killed in the accident and ₹50,000 each for those injured.