Indian Army personnel along with Engineer Task Force opened the mouth of the tunnel at Tapovan in the flood-affected Uttarakhand's Joshimath as rescue operations continued more than 24 hours after the disaster hit.
A senior Indian Army official said: "Rescue work continued throughout the night with earthmovers by installing generators and searchlights."
The rescued people were given medical aid at the field hospital created by the army at the site.
Indian Air Force helicopter sorties were carried out for insertion of rescue teams before first light. "Reconnaissance of higher reaches were also made to detect any avalanche threat," said a senior officer.
Around 150 people were feared dead in the flash flood that devastated the National Thermal Power Corporation (NTPC) Limited project on river Dhauli Ganga near Tapovan.
"An avalanche near Tapovan in Uttarakhand has damaged a part of our under construction hydropower project in the region. While rescue operation is on, situation is being monitored continuously with the help of district administration and police," the NTPC said in a statement on Sunday.
The flash flood occurred in river Rishi Ganga near Joshimath around 10.45 a.m. on Sunday after a part of a glacier fell in the river exponentially increasing its volume.
Due to this, the Rishi Ganga hydro project near Reni village was completely devastated.
The Border Road Organisation (BRO) bridge on Joshimath - Malari highway was also completely washed away.
"There were six grazers with their livestock and they were also taken away by the flash flood," said local administration.
Rishi Ganga meets Dhauli Ganga near Reni village due to which Dhauli Ganga also flooded. Around six houses of the village also washed away.
Further two bridges connecting villages on the other side of river also got washed away.
The BRO has managed to clear and reopen the Rishikesh-Joshimath-Mana road which was blocked at Hathipahad due to the flash flood.
The National Disaster Response Force, Indo-Tibetan Border Police and state authorities have been carrying out rescue operations along with the army in the region. The Central government is monitoring the situation and joint efforts of all the agencies are being made to rescue those trapped.