India’s Kolkata Metro Rail (KMRC) is set to complete the development of the country’s first underwater metro service by December 2023.

The upcoming project, called East-West Metro Corridor, will pass through the Hoogly river and link Howrah with Kolkata, reported ANI.

The project will be developed at a cost of more than Rs80bn ($967m), according to Times Now.

KMRC general manager civil Shailesh Kumar said: “The ongoing underwater tunnel project is likely to be completed by December 2023.”

In 1984, Kolkata Metro became operational. Currently, the metro is said to offer services to the entire city of Kolkata and its adjacent areas.

Regarding the delay in completing the East-West Metro Corridor project, Kumar said: “Some rehabilitation works are in process and other issues are delaying the completion of the underwater metro project.”

KMRC has used German machines and other experts to build the tunnel, work inside of which is still undergoing.

Kumar was quoted by ANI as saying: “We have taken foreign experts in tunnelling projects, currently we are using machines from abroad (German) to make the difficult task easier.”

The metro tunnel construction cost is around Rs1.2bn per kilometre, which goes up to around Rs1.57bn per kilometre during the construction of the tunnel underwater.

KMRC added: “We have made only 520m-long tunnel under the river (Hooghly) which was a very challenging task but we did it.”

Once completed, the project will allow passengers to travel under the water for a stretch of half a kilometre within less than one minute.

It is also expected to ease traffic congestion by connecting Howrah and Sealdah railway stations in addition to Kolkata Metro’s north-south line at Esplanade.