NEW DELHI — Four days after 40 workers became trapped in a Himalayan road tunnel, Indian authorities were still trying Thursday to find a way through debris and rescue them, as anguished family members and colleagues protested outside to demand faster action.

The workers became stranded Sunday about 500 feet from the tunnel’s entrance after landslides in the northern Indian state of Uttarakhand caused a partial collapse. Communication was severed, leaving the men inside, unsure of what would happen.

In the hours afterward, officials established contact with the workers by sending radios through an undamaged pipe into the tunnel. Later, a bigger pipe, 35 inches in diameter, was inserted, but falling debris injured two rescue workers and delayed the operation. Food, water and oxygen were sent through another pipe with the help of compressors. Authorities have said the men are safe inside the tunnel.

Officials put dozens of rescuers to work around the clock to remove debris using drilling equipment and excavators. But they abandoned those efforts after a heavy drilling machine failed to create an escape passage, but caused more debris to fall into the tunnel, said Arpan Yaduvanshi, a police official in Uttarkashi District, site of the rescue operations.

Indian officials said Thursday that they were trying a different tack, working to deploy an advanced machine that could cut through the debris. “We are inserting steel pipes into the rubble to create a passage for the workers to come out,” said Ranjit Sinha, a top disaster management officer in Uttarkashi. The plan was for the men to crawl through the pipe, getting around the problem of falling debris.

The high-powered auger drilling machine was being assembled after it was airlifted from New Delhi. The machine will cut through the debris at more than double the rate of the previous drilling machine, officials said, adding that they hoped to reach the workers by Friday.

India has sought advice on the operation from a company based in Thailand that helped rescue children from a flooded cave there in 2018. Officials said they were also in touch with engineering experts at the Norwegian Geotechnical Institute.

Uttarakhand attracts hundreds of thousands of Hindu pilgrims every year and has also become a major tourist attraction. In recent years, the mountainous state has experienced a boom in construction of buildings and roadways.

The construction was being done in a landscape that has become increasingly fragile for large development projects as glaciers quickly melt.

Environmentalists and experts appointed by India’s top court have criticized the federal government for going ahead with the project despite their ecological concerns. Throughout the year, landslides and flooding caused by heavy rains have led to large-scale infrastructure damage, killed dozens and washed away entire villages.