Rescue workers renewed efforts on Thursday to reach 40 men trapped inside a collapsed highway tunnel in India for the fifth day, making slow progress as they began drilling through rock and soil debris.

Authorities said they were confident an advanced drilling machine flown in from New Delhi will speed up the rescue at the site in the northern state of Uttarakhand.

The plan is to drill and create space for a pipe that can be used by the trapped men to crawl to safety.

Drilling had penetrated about 3 metres (10 ft) of debris by on Thursday morning, officials said, adding that they had to cover a total distance of about 60 metres.

The machine can drill through about 2-2.5 metres of rock per hour, Ranjit Sinha, the state’s top disaster management officer, said.

Two of the trapped construction workers were treated for nausea and headache as they endured a fifth day confined to a small space behind the rubble, officials said.

“There is electricity, water and we are sending food. The new machine which is more powerful and speedy, is deployed,” V.K. Singh, federal deputy minister for road transport and highways, and a retired army chief, told reporters at the site.

“Our priority is to save them all. The morale of people trapped inside is high. We are very optimistic of bringing them out,” he said.

Singh said Indian agencies involved in the rescue effort were consulting experts in Austria, Norway and Thailand, but did not elaborate.

Asked about local media reports which said India had consulted Thai experts involved in the 2018 rescue of 12 boys trapped in a cave complex, Uttarakhand Chief Minister Pushkar Singh Dhami said: “Technical experts who have dealt with such situations in foreign countries have also been consulted.”

Ambitious project

The 4.5 km (3 mile) tunnel is part of the Char Dham highway, one of the most ambitious projects of Prime Minister Narendra Modi’s government. The $1.5 billion project aims to connect four Hindu pilgrimage sites through 890 km (550 miles) of roads.

Since the tunnel collapsed, the trapped men have been supplied with food, water and oxygen via a pipe and they are in contact with rescuers via walkie-talkies.

“Two of them, who complained of nausea and minor headache, were given medicines through the pipe and are fine now,” Arpan Yaduvanshi, a local police officer said.

Local media reported that a six-bed makeshift hospital had been put in place near the tunnel to cater to any medical attention the men might need once they are rescued.

Authorities have not said what caused the tunnel to cave in but the region is prone to landslides, earthquakes and floods. The highway project has faced some criticism from environmental experts and some work was halted in January after hundreds of houses along the routes were damaged by subsidence.

The federal government has said it employed environmentally friendly techniques in the design to make geologically unstable stretches safer.