On 9 July 2025, the first major breakthrough was achieved in the 21-kilometre tunnel being built between Bandra-Kurla Complex (BKC) and Shilphata in Maharashtra, with the successful completion of a 2.7-kilometre continuous section.

Out of the total tunnel length, 5 kilometres is being constructed using the New Austrian Tunnelling Method (NATM) between Shilphata and Ghansoli, while the remaining 16 kilometres will be executed with Tunnel Boring Machines (TBMs). The tunnel also features a 7-kilometre undersea stretch beneath Thane Creek, a first of its kind in India.

To accelerate progress in the NATM section, an Additionally Driven Intermediate Tunnel (ADIT) was created, allowing parallel excavation from both Ghansoli and Shilphata. To date, approximately 1.62 kilometres has been excavated from the Shilphata side, with total NATM progress reaching around 4.3 kilometres.

Extensive safety systems have been installed on-site, including ground settlement markers, piezometers, inclinometers, strain gauges, and biometric access controls. These are designed to ensure secure tunnelling without disrupting surrounding structures or habitats.