The ground report: Going deep inside Mumbai's under-river metro tunnel

There is a steady clanking of metal chains. Labourers are busy at work, fixing disc cutters onto Tansa, under Mumbai's Mithi river. About 24 kilometres away, near Mumbai's Taj Vivanta, is Surya, tasked with another tunneling work.

Surya and Tansa are part of a fleet of tunnel boring machines (TBM), requisitioned for the Rs 30,000-crore underground transit network — the third line of the Mumbai Metro.

At the southern-most end of the city, Cuffe Parade metro station is under construction opposite Taj President. Temporary scaffolding is used to reach 23 metres beneath the base level, where metro rail tracks will be laid.