The recovery of five bodies on Saturday takes the toll in the tragedy to 67 while 137 are still missing.
Uttarakhand Irrigation Minister Satpal Maharaj revived the debate about a lost nuclear device to be the reason behind the flash floods.
After drilling the tunnel ground 12 meter deep and 75mm in diameter, the NTPC began widening it to almost one foot which is estimated to take 8 more hours.
A warning was issued to evacuate the rescue spot and leave for high grounds just in case another flash flood comes.
The development took place after a combined meeting of state government authorities, armed forces and the NTPC.
Two persons who were listed as missing in the avalanche and flash floods in Uttarakhand returned to their homes safely on Wednesday.
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Relief is being distributed by helicopters among villagers cut off due to the washing away of a bridge in the avalanche at Malari.
Kedarnath MLA Manoj Rawat said excavators and Pokland machines should be brought in to speed up the process.
Officials from the Army Medical Corps of the Indian Army said that they have been trapped without food, water and heat in the tunnel where temperatures plummet to as low as 2 degrees.
People from different parts of the country have gone missing in the tragedy, including 19 from Datunu village of the Jaunsar area in Dehradun district.
Necessary supplies and medical assistance are being provided to these villages through helicopters, Union Home Minister Amit Shah said.
In a bid to save the men trapped in the tunnel, the ITBP used ropes, pulleys, carabiners and spades to descend into the muck.
People can register information about their missing family members on helpline 1070 and on WhatsApp number 9454411036.
Uttar Pradesh government releases helpline numbers, extends help to Uttarakhand in carrying out the rescue and relief operation.
Abrupt snowslide, not glacier burst, might have caused the calamity: Uttarakhand CM Trivendra Singh Rawat
Trivendra Singh Rawat made the statement on the cause of the tragedy after holding a meeting with ISRO scientists and officials of the Army and ITBP.