The state cabinet, at its meeting slated for this week, is expected to approve the proposal.

Several reasons are being cited for the increase, including the time taken in excavation owing to the presence of basalt rock, adoption of bottom-up construction technology for want of space, additional cost incurred on account of rocky layers and the need to dispose of them, and the need to erect temporary steel decks for road traffic to allow construction of underground stations, as many of them are in congested areas.

Yet another reason for the cost escalation is that Metro 3 stations have to accommodate eight coaches as against the six used by the Delhi Metro. Moreover, labour and accommodation are more expensive in Mumbai.

The state government’s approval came days after it allowed the Mumbai Metro Rail Corporation (MMRCL) to resume work on the Metro 3 car shed at Aarey Colony in Goregaon (East).

A senior official with the state urban development department said the loan needed for the project from the Japan International Cooperation Agency (JICA) has increased by Rs 66.89 billion to Rs 199.24 billion.

The state government will have to bear an paltry additional cost of Rs 1.33 billion as its contribution has gone up to Rs 25.54 billion from Rs 24.21 billion. But its share capital in the project will have to be increased to Rs 36.99 billion from Rs 24.02 billion. This amount will come from the Mumbai Metropolitan Region Development Authority (MMRDA) and is to be used for land acquisition, rehabilitation and tax.