Howrah Maidan: East-West Metro trains will start plying between Howrah Maidan and Salt Lake Sector V by December 2020, officials said on Friday after completion of tunnel-boring work under a part of Calcutta which is dotted with dilapidated buildings and heritage structures.

Officials of Kolkata Metro Rail Corporation (KMRC), the implementing agency of the most ambitious infrastructure project in recent years, said the December 2020 "deadline" was unlikely to be missed.

The project has missed several deadlines because of land logjams at multiple points.

"Now that all the hurdles have been cleared and the most difficult stretch for the tunnels behind us, we are expecting to get all infrastructure ready and run trains along the entire stretch by December 2020. The deadline is unlikely to be missed," a KMRC official said while supervising work at Howrah Maidan, the western end of the tunnels.

One of the two tunnel-boring machines touched the western diaphragm wall of the proposed New Mahakaran station on Friday. The other one did so a few days ago.

Friday marked the end of a critical stage of building the 14.65km link between Howrah Maidan and Sector V - digging the tunnels under the central business district, which is packed with crumbling edifices and heritage structures such as Writers' Buildings and Currency Building.

"We have successfully completed the 2.9-km tunnelling between Howrah Maidan and New Mahakaran stations," the official said.

The tunnel-boring machines will now move towards the site of the proposed Esplanade station, around 750m from New Mahakaran.

A trolley carried the soil excavated by the machine that touched the New Mahakaran diaphragm wall on Friday to the underground site where Howrah Maidan station will come up, sparking celebrations among officials and engineers.

From the Howrah Maidan station site, the soil is lifted by cranes and dumped at designated places.

"The tunnel-boring machines had to move fast under the buildings in the Brabourne Road-BBD Bag area to ensure that cracks did not appear on the walls, floors and ceilings. It depended on quick disposal of the muck," said an official of Afcons, the private company digging the two tunnels.