The Rs 6.48bn ($US 98m) project involved construction of a new alignment for the first 100km between Lumding and Migrendisa which runs parallel to the former metre-gauge line and crosses the original formation in several locations. The line then diverges for 30km before rejoining the former metre-gauge alignment near Ditockechera.

Freight trains have been operating on the line since the end of March and the Ministry of Railways says the completion of the project will enable the passenger service to be stepped up in future.

Phase 2 of the project will be completed by the end of March 2016 and covers the conversion of the 118km Badarpur - Kumarghat line as well as three branches: Arunachal - Jiribam (50km); Baraigram - Dullabcherra (29km) and Karimganj - Mahishasan (13.5km).

Prabhu says enhancing rail links to northeast India is a priority for the national government, which allocated Rs 52bn to rail projects in the region in the 2014-2015 financial year, with a further Rs 53bn assigned for 2015-2016. Gauge conversion in northeast India has averaged around 133km per year over the last 4-5 years, but according to Prabhu this will reach a record high of 550km this year.

Earlier this year through services were launched between Dehli and Itanagar, the state capital of Arunachal Pradesh, following the completion of a project to convert the 510km Rangiya - Rangapara - Murkongselek line from metre to broad-gauge.

Last month the line from Badaprur to Agartala, the capital of Tripura state, was closed for gauge-conversion, which will be completed by next March. The conversion of the Kathakal - Bhairabi and Arunachal - Jiribam lines will also bring the states of Mizoram and Manipur onto the national broad-gauge network.