India has sought advice from the Thai company that rescued children from a flooded cave in 2018 as it races to save 40 men trapped in a road tunnel, officials said Wednesday.

Excavators have been removing debris since Sunday morning from the site in the Himalayan state of Uttarakhand to create an escape tunnel for the workers, all of whom are still alive.

Officials have "contacted the Thai company which rescued the children trapped in the cave", the state government's department of public relations said in a statement.

The statement was referring to the dramatic operation to rescue 12 boys from a junior football team and their coach who were trapped for more than two weeks in the Tham Luang cave complex.

No other details were given.

Authorities have also asked for help from engineering experts in soil and rock mechanics at the Norwegian Geotechnical Institute as frantic efforts to free the men stretched into a fourth day.

Rescuers said on Wednesday they had sent medicine to the 40 men, trapped since the road tunnel they were building collapsed on Sunday.

"After consultation with doctors, medicine has been sent to the workers through pipes," police officer Prashant Kumar told AFP from the site. "Contact is being maintained with the workers."

No details were given about the condition of the men or how many of them were sick.

Food and oxygen had also been sent to the trapped workers, he said.

- 'War footing' -

But as rescue teams removed the vast piles of rubble, more fell from the broken roof of the tunnel and two labourers working to remove the debris were injured overnight Tuesday, Kumar said.

The pace of drilling was "slow because of natural causes", but efforts were being made on a "war footing", Uttarakhand state police chief Ashok Kumar said in a statement on Wednesday.

The air force on Wednesday flew in a second drilling machine on a C-130 Hercules military plane on Wednesday to "speed up rescue work" after the first one broke down, he said.

Dozens of colleagues of the trapped workers protested outside the tunnel on Wednesday, blaming authorities for "slow rescue work", one of the protesters told AFP.

Photos released by government rescue teams soon after the collapse showed huge piles of rubble blocking the wide tunnel, with twisted metal bars from its roof poking down in front of slabs of concrete.

- 'Patience and trust' -

Engineers are using heavy machinery to drive a steel pipe about 90 centimetres (nearly three feet) wide through the debris, wide enough for the trapped men to squeeze through.

"We should keep our patience and trust," Ashok Kumar said. "I am sure that we will rescue all the labourers."

The 4.5-kilometre (2.7-mile) tunnel was being constructed between the towns of Silkyara and Dandalgaon to connect Uttarkashi and Yamunotri, two of the holiest Hindu shrines.

The tunnel is part of 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 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.

Construction worker Hemant Nayak told AFP that he had been in the tunnel early on Sunday when the roof caved in, but he had been on the right side of the collapse and escaped.

Small amounts of dirt had been falling into the tunnel but "everyone took it lightly", he told AFP on Tuesday.

"Then suddenly a huge amount of debris came and the tunnel was closed."

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