The under-construction Mumbai - Ahmedabad High Speed Rail Corridor (MAHSR) is a highly anticipated rail network line. It is slated to include India’s 1st 21 km long tunnel, with a distance of 7 km under the sea.

On June 8, National High Speed Rail Corporation Limited (NHSRCL) signed an agreement with a Shapoorji Pallonji subsidiary, Afcons Infrastructure for the construction of this undersea tunnel. The contract is valued at ₹6,397 crores.

Located at the Thane Creek near Mumbai, the tunnel will have underground stations at Bandra-Kurla Complex and Shilphata. To be a single tube structure, it will accommodate twin tracks for upward and downward movement of trains.

Three tunnel boring machines (TBMs) with a cutter head of 13.1 metre diameter will be used for boring 16 km of the tunnel portion, while the remainder 5 km will be done using New Austrian Tunnelling Method (NATM).

Once completed, the tunnel will run from a minimum depth of 25 metre to a maximum depth of 65 metre from the ground level. Additionally, more than 60 km of viaduct in Gujarat has been completed, while preliminary work has commenced near Bandra-Kurla station. The trial run of the bullet train is anticipated to take place between Surat and Bilimora in 2026.