The 52 km long rail line connecting Sevoke in West Bengal with Rangpo in Sikkim is now projected to be operational by December 2023.
The construction of the rail line, which will have six stations, started in 2009.
It was initially scheduled to be completed by 2015 but has been facing challenges due to difficult terrain and land-related hiccups, which caused a delay in the project.
The estimated cost of the project has also increased from Rs 1,300 crore to over Rs 5,000 crore.
The Indian Railway Construction Company, which is implementing the project, said that 30 percent of the work has been completed so far.