Rescue operations to evacuate 41 workers trapped in Uttarakhand's Silkyara tunnel resumed on Thursday morning after an overnight hurdle delayed the drilling by several hours.

Former advisor to the prime minister's office Bhaskar Khulbe, who was at the site, said an iron mesh which had come in the path of the drilling machine that is creating an escape path for the workers was removed in the morning.

This held up the drilling through the 57-metre stretch of the rubble of the collapsed section of the tunnel by six hours, dampening somewhat the previous evening's enthusiasm over an imminent rescue.

Removing the mesh in a claustrophobic environment inside the pipe was difficult and the problem was compounded by the lack of oxygen, Khulbe told reporters.

The workers have been trapped for 11 days after a portion of the under-construction tunnel on the Char Dham route collapsed.

At 10 am Thursday, Khulbe told reporters it would take 12 to 14 hours of drilling -- which was set to resume after the metal hurdle was cleared -- to insert six-metre sections of a steel pipe into the passage.

The National Disaster Response Force (NDRF) will then enter the steel pipe and help bring up the trapped workers, one by one. They would lie on wheel-fitted low-height stretchers which will be pulled out of the tunnel.

This process is likely to take another three hours, Khulbe said.

They are being sent food, medicines and other essentials through a new six-inch wide tube, which is also used for communication, and a thinner tube that existed earlier.

Khulbe said the process of welding the pipes to go beyond 45 metres has been restarted. The drilling will also resume soon, he said.

Union Minister of State for Road Transport and Highways Gen V K Singh and NDRF Director General Atul Karwal are in Silkyara for an on-the-spot review of the rescue efforts.

Chief Minister Pushkar Singh Dhami also arrived in Silkyara and spoke to the trapped workers, the NDRF DG said, adding the workers are fine.

"Another pipe has been drilled and the length achieved so far is 48 metres. The next pipe is being welded now. We plan to drill two more pipes so that we achieve a length of up to 60 metres through the rubble to get some extended space," Karwal said.

If no other obstruction is encountered during drilling, the operation would likely get over by Thursday night, he said.

Three scientists from the Central Institute of Mining and Fuel Research, Roorkee, including tunnel expert R D Dwivedi are also at the site to take updates on the rescue operations.

International tunnelling expert Arnold Dicks, who is present at the site, said, "It seems we have reached the door and knocking at it. We know people are at the other side of the door. I will go in and see what is happening."

Till 6 pm on Wednesday, up to 44 metres of the escape pipe had been inserted into the debris, an official update said in Delhi.

The drilling of 800 mm diameter pipes from the Silkyara end was put on hold on Friday afternoon when the American-made auger machine encountered a hard obstacle around the 22-metre mark, creating vibrations in the tunnel that caused safety concerns.

The drilling resumed around midnight Tuesday.

As the machine drills through, six-metre sections of steel pipes, just under a metre wide, are pushed into the escape passage. Once the pipeway reaches the other end, the trapped workers are expected to crawl out.

Uttarkashi Superintendent of Police Arpan Yaduvanshi said the post-rescue plan is ready to provide immediate medical care to the evacuated workers.

"When the workers come out, they will be taken via the green corridor under police escort in ambulances to Chinyalisaur CHC where all facilities have been created for them," the officer said.

Forty-one ambulances are waiting outside the tunnel to rush the workers to the 41-bed separate ward set up at the Community Health Centre in Chinyalisaur.

Meanwhile, relatives of the trapped workers waiting in Silkyara expressed hope that the rescue operation will end by Thursday night with their safe evacuation.

Haridwar Sharma whose brother Sushil Sharma is among the trapped workers said he had spoken to him and he was fine.

"All is well. They have been served food in the night and milk in the morning. They are fine. We are sure they will be evacuated, " he said.

Sudhanshu Shah whose brother Sonu Shah is among those trapped said as the tunnel collapsed on the morning of Diwali, he did not celebrate the festival and will do so only when his brother comes out.