Indian rescuers said on Friday they had drilled less than halfway through the debris to reach 40 men trapped in a collapsed tunnel for nearly a week.

A second heavy drill is to be airlifted into the northern state of Uttarakhand after the existing giant machine — itself flown in as a replacement by the air force on Wednesday — hit a boulder, officials said.

Excavators have been removing debris since Sunday morning to create an escape route for the workers after a portion of the tunnel they were building collapsed in the Himalayan state of Uttarakhand.

Rescue efforts have been slowed by debris that has continued to fall.

Engineers are trying to drive a steel pipe about 90 centimetres wide through the debris — wide enough for the trapped men to squeeze through.

“Drilling has been done up to 24 metres for safe extraction,” Anshu Manish Khalko, director of the government’s highways and infrastructure corporation told reporters on Friday afternoon.

But he said around 36 metres of pipe still needed to be laid to reach the workers.“That may take time”, he said, without giving further details.

After the first earth-boring drill developed problems, the air force on Wednesday flew in a second machine on a C-130 Hercules military plane. The giant drill bit stretched much of the length of the aircraft’s cargo hold.

Field hospital

As rescuers race to save the men, India has sought advice from the Thai company that rescued children from a flooded cave in 2018, as well as engineering experts in soil and rock mechanics at the Norwegian Geotechnical Institute.

Rescuers have been communicating with the trapped men using radios.

Food, water, oxygen and medicine have also been sent to the trapped workers viaa 15-centimetre-wide pipe.

No official details have been given about the condition of the men, but local media reported that some were suffering from vomiting, headaches, anxiety and stomach problems.

A six-bed field hospital has also been set up outside the site with ambulances on standby to transfer serious cases to a proper hospital.

The 4.5 kilometre tunnel was being constructed between the towns of Silkyara and Dandalgaon to connect Uttarkashi and Yamunotri, two of the holiest Hindu sites.

The tunnel is part of Indian Prime Minister Narendra Modi’s road project aimed at improving travel conditions between some of the most popular Hindu shrines in the country as well as in areas bordering China.

Experts have warned about the impact of extensive construction in Uttarakhand, where large parts of the state are prone to landslides.

Accidents on big infrastructure projects are common in India.

In January, at least 200 people were killed in flash floods in ecologically fragile Uttarakhand in a disaster that experts partly blamed on excessive development.