Mumbai, Nov 11 (IANS): Work on the upcoming Mumbai Metro Line 3 entered a crucial stage with excavation work started by a Tunnel Boring Machine in Mahim on Friday, officials said.

This is the first of the three TBMs which have already been lowered in launching shafts, one at Azad Maidan in south Mumbai and two in Mahim.

These TBMs will carry out boring 25-30 metres below the ground level in what is mostly rocky strata on the entire Metro Line 3 corridor, which will be the city's first running fully underground.

Top officials including Mumbai Metro Rail Corporation Managing Director Ashwini Bhide and others were present to witness the first excavation work by the TBM at Nayanagar.

The Line 3 will run between 33.50 km between Colaba-Bandra-SEEPZ with two underground stations and one at ground level, totally costing a little over Rs 23,000 crore.

For this, the Mumbai Metropolitan Region Development Authority has imported at least 17 TBMs, of which four have already arrived and the remaining 13 are expected by February next.

The TBMs shall be launched through seven shafts and start boring the metrol tunnels from various points like Cuffe Parade, Chhatrapati Shivaji Maharaj Terminus, Mumbai Central, Worli, Bandra Kurla Complex, Mumbai Airport and Marol Naka.

The entire tunneling activity is likely to be completed within two years and the Metro Line 3 is expected to be operational on schedule by December 2021, said a MMRDA spokesperson.