A portion of an under-construction tunnel between Silkyara and Dandalgaon on the Brahmakhal-Yamunotri National Highway collapsed early on Sunday, trapping around 40 workers inside, officials in Uttarkashi said.
Personnel from the National Disaster Response Force, State Disaster Response Force and police launched a search and rescue operation immediately after being informed of the accident, superintendent of police (Uttarkashi) Arpan Yaduvanshi said.
Quoting officials from National Highways & Infrastructure Development Corporation Limited, which is building the tunnel, Yaduvanshi had initially put the number of labourers trapped in the tunnel at 36.
However, the District Emergency Operation Centre later released a list of 40 labourers trapped inside.
They are from Bihar, Jharkhand, Uttar Pradesh, West Bengal, Odisha, Uttarakhand and Himachal Pradesh.
Oxygen is being pumped into the collapsed section of the tunnel, which is part of the Char Dham all-weather road project, through a water pipe so that the trapped labourers do not have difficulty breathing, Yaduvanshi said.
The rescue operation has been going on for the past 12 hours but without any breakthrough so far.
However, those trapped inside have sent out signals that indicate they are safe, an official at the site said.
"We are removing the muck to measure how deep the point where they are trapped is. It does not seem too long. We hope to reach them soon. However, there are indications that they are safe as they appear to have released some water through an outlet," Rajesh Panwar, the Navyuga Construction Company project manager, said.
About 160 rescuers are trying to reach the trapped labourers with the help of drilling equipment and excavators, the District Emergency Operation Centre said.
Some more equipment such as a vertical drilling machine are about to reach the site to assist the rescue efforts.
Border Roads Organisation and Indo-Tibetan Border Police teams led by Commanding Officer Naman Narula and Assistant Commandant Jadhav Vaibhav were roped in later to assist the rescue efforts, the officials said.
Uttarkashi District Magistrate Abhishek Ruhela, National Highways Authority of India chief general manager Vishal Gupta and NDRF Second-in-Command Ravishankar Badhani are on the spot to supervise the search and rescue operation.
Chief Minister Pushkar Singh Dhami spoke to Ruhela for an update on the situation and asked him to speed up the rescue operation.
Ruhela has cancelled the Diwali holiday of employees in the departments concerned.
"I am in touch with the officials on the spot and constantly monitoring the situation. I have asked them to expedite the rescue efforts. I pray everyone is rescued safely," Dhami said in a post on Facebook.
According to Yaduvanshi, the incident occurred between 6 and 7 am.
The collapsed portion of the tunnel is located about 200 metres from the entrance, he said, adding food items are also being sent in and the workers will be rescued soon.
On the circumstances that led to the collapse, he said the priority is to save the lives of those trapped inside.
"What led to the incident, fixing responsibility, etc will come later. Saving the lives of those trapped inside is our first priority," Yaduvanshi said.
The proposed tunnel, which is part of the Char Dham road project, will reduce the journey from Uttarkashi to Yamunotri by 26 kilometres.
