Rescuers in India are set to work through Thursday drilling through debris to reach 41 men trapped in a highway tunnel in the Himalayan region after removing a metal obstruction that slowed progress overnight, a top official said.

The men have been stuck in the 4.5-km (3-mile) tunnel in Uttarakhand state for 11 days since it caved in early on Nov. 12 and are safe, authorities have said, with access to light, oxygen, food, water and medicines.

Rescuers had expected to break through early on Thursday as only the last third of the debris blocking the tunnel remained to be drilled through before an evacuation pipe could be pushed in and the men pulled to safety.

But they encountered a lattice steel girder arch after covering 45 metres (150 ft) of the estimated 60-metre (197-ft)stretch of debris, which required about six hours to cut and remove, said the official, Bhaskar Khulbe.

"Our calculation as of now is ... roughly about 14 to 15 hours, unless something else happens, and we hope we will be able to do that," Khulbe, who works on the tunnel project, told reporters.

"It is difficult to anticipate what more hurdles we might face," he said, adding that since the structure was not one of very hard rock, no major problem was expected, apart from another metal obstacle or rock.

Once the drilling is completed, officials plan to send rescuers through the evacuation pipe with stretchers on wheels to bring out the trapped men, they said.

Authorities have not said what caused the tunnel collapse, but the region is prone to landslides, earthquakes and floods. Efforts to bring the men out have been slowed by snags in drilling in the mountainous terrain.

The collapsed tunnel is located on the Char Dham pilgrimage route, one of the most ambitious projects of Prime Minister Narendra Modi's government.

It aims to link four important Hindu pilgrimage sites with 890 km (550 miles) of two-lane road, being built at a cost of $1.5 billion.

On Wednesday the government said the National Highways Authority of India would do a safety audit of 29 tunnels it is building following the collapse.

(Writing by YP Rajesh)