The tunnel in Sikkim where the accident took place was started 21 years ago.
A major accident has occurred in an under construction tunnel in Namchi district of Sikkim. This tunnel is part of NHPC’s Teesta Stage-VI Hydroelectric Project. The place of the accident is in Samardung, Jholungey area. So far 8 people have died in this accident. Relief and rescue work is going on at the spot. Come, let us understand what this tunnel project is? When did the work start? When is the work expected to be completed? How is this tunnel to be used? How is it going to be useful to the common people?
The full name of this project is Teesta Stage-VI Hydroelectric Project. Its installed power capacity is 500 MW. NHPC is developing the project. NHPC is the premier hydropower company of the Government of India. The project is being built to harness the hydropower of the Teesta river basin.
This is a run-of-the-river project. This simply means that the flowing water of the river will be used to generate electricity. In this, there is no plan to stop the water for a long time by building a huge reservoir. The main area of the project is near Sirwani village in Sikkim. The tunnel where the accident occurred is in the Samardung-Jholungey area. Different construction sites and entryways connect different parts of the project.
Construction started 21 years ago
This project was started in the year 2005. At that time the Sikkim government had given it to Lanco Teesta Hydro Power Limited. The project was initially targeted to be completed by 2012, but the construction work could not be completed on time. Financial problems arose. Issues related to forest clearance came to the fore. Hilly geology and weak rock conditions also became challenges. The earthquake of 2011 also had an impact on the project. After this the parent company went into financial trouble.
The project, which started in 2005, was initially targeted to be completed by 2012. Photo: PTI
In the year 2018, bankruptcy process started against the company. Then NHPC proceeded with the process of acquiring the project. After the approval of the Central Government in March 2019, NHPC got the responsibility of completing the incomplete work. At that time only about 30 percent work of the project was completed. NHPC then stated the need for a new plan and tender process for the remaining work. Therefore the story of construction can be understood in two phases. The first phase started in 2005. The second phase proceeded from 2019 after NHPC took over.
The cost of the project is increasing
The initial estimated cost of the project was Rs 5,748.04 crore. This estimate was based on the prices of July 2018. This also included the cost of acquisition of the project. Later the cost increased. Delays, difficult geographical conditions, new construction work, inflation and project related challenges could be the reasons for this. In a report dated December 2025, the cost of Teesta-VI was put at Rs 8,449 crore. In the same report, the target has been stated to make it operational by September 2029. Further changes in cost are possible. The reason for this could be the progress of construction, security arrangements, weather and Himalayan geological challenges.
Rescue mission is going on for rescue. Photo: PTI
Main structure of tunnel and project
In the project, about 26.5 meter high barrage is being built on Teesta river. Barrage will control the flow of water. After this the water will be transported through tunnels to the underground power house. There are two main head race tunnels in this project. The shape of both is like a horseshoe. The diameter of each tunnel is about 9.8 meters. The length of each is about 13.76 kilometers. Water will go from these tunnels to the underground power house. Four power generation units are to be set up there. The capacity of each unit will be 125 MW. In this way the total installed capacity will be 500 MW. Breakthrough was reported to be achieved in parts of the project’s head race tunnel in March 2026. Breakthrough means that the excavations going on from two directions merged together. This is an important technical stage of tunnel construction.
What facilities will be available upon completion?
Upon completion of the project, it will have the capacity to generate 500 MW electricity. This electricity is mainly seen as a source of clean energy. In hydroelectric projects, electricity is not generated by burning coal or gas. It is estimated that the project can generate about 2,400 million units of electricity in a normal year. This will provide additional electricity to the national electricity grid.
The energy system of the North-Eastern region can also be strengthened. Sikkim will get a share of free electricity from this project. There is a provision for the state to get 12 percent of the production as royalty for the first 15 years. After this this share can be 15 percent. The remaining electricity will be available for sale. Some employment opportunities will also increase once the project starts.
There are many big questions on security
The recent accident has raised questions on the safety arrangements in the projects under construction. Especially in the Himalayan states, dangers like rain, landslides, weak rocks and underground gas are serious. Gas testing, ventilation, emergency exits, communication systems and rescue equipment are extremely important for the people working inside the tunnel. Regular geological study is also necessary. Only an official investigation into the causes of the accident will clarify which factors were responsible for the collapse of the tunnel and the gas situation. At present this project is included in the big power projects of Sikkim, but the accident has made it clear that along with the speed of construction, the safety of the workers will also have to be kept on top.
Rescue mission continues after the accident
#WATCH | Rescue operations are underway in Sikkim’s Namchi district after a tunnel collapsed, trapping at least 12 workers. More details awaited
(Video Source: Sikkim Police) pic.twitter.com/3TpH6YTyRV
— ANI (@ANI) July 20, 2026
How did the accident happen?
The accident happened on Monday i.e. 20th July in the afternoon. It was raining continuously in the area. Meanwhile, debris and rocks slipped from the hill and came to the mouth of the tunnel. The entry way was closed. It became difficult for the people working inside to come out. Another serious problem made the relief work difficult. Officials suspected the presence of gas inside the tunnel. Some rescue workers experienced dizziness and fainting while going inside. It was said in the news that this gas may be coming out from the rocky layers inside the ground. There is a possibility that these layers may have been affected by landslides. Rescue efforts were slowed by rain, poor terrain, limited visibility and the threat of gas. Teams of NDRF, SDRF, police, fire department and district administration were deployed on the spot.
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