“If there is no blockage, we hope there could be happy news late tonight or tomorrow,” Ahmad told reporters at the site.
“This is very happy news for us, that we are moving forward at a fast pace,” he added.
However, he warned that the remaining section yet to be drilled was critical.
Rescue efforts have been slow, complicated by falling debris as well as repeated breakdowns of crucial heavy-drilling machines.
The giant earth-boring machine last week ran into boulders, and drilling was put on hold for more than three days after a cracking sound in the roof.
Uttarakhand chief minister Pushkar Singh Dhami on Wednesday spoke of the “positive progress made in the last 24 hours”, without further details.
But a government statement also noted that “timelines provided are subject to change due to technical glitches, the challenging Himalayan terrain, and unforeseen emergencies”.
In case the route through the main tunnel entrance does not work, blasting and drilling have also begun from the far end of the unfinished tunnel, nearly half a kilometre long. Preparations have also been made for a risky vertical shaft directly above.