Fears are mounting for 40 construction workers in India who have been stuck in a collapsed tunnel for more than 72 hours, as rescue efforts are hampered by fresh debris and those inside begin reporting illness. The road tunnel, which was under construction in the mountainous state of Uttarakhand, collapsed in the early hours of Sunday after a landslide. Dozens of migrant labourers were trapped 200 metres inside as the part of the roof caved in and the tunnel entrance was blocked by concrete rubble, rocks and twisted metal. Since Sunday, a huge rescue operation has been under way involving heavy machinery, more than 200 disaster management and rescue officials and engineers working to clear the debris. More than 20 metres of rubble has been cleared, but 30 metres more needs to be removed to reach the men. The local district magistrate Abhishek Ruhela told reporters that “if everything goes as planned, the trapped labourers will be evacuated by Wednesday”. On Tuesday metre-wide metal pipes were brought to the site in the hope of drilling a shaft through the debris and inserting the pipes, creating an escape passage for the workers. However, rescue efforts were set back as more boulders continued to fall and there was a fault with the drilling machinery. The authorities said a more powerful drill was airlifted from Delhi on Wednesday morning to assist with the operation. But officials warned that if the machinery did not work, it could be several more days before they could reach the workers. “These are challenges in such rescue operations, but we will overcome them,” said Ranjit Sinha, a disaster management official. Oxygen and food packets containing dried chickpeas, dried fruits, almonds and puffed rice have been funnelled to the 40 labourers through small pipes inserted into the cavity where the men are trapped. Contact has been maintained through walkie-talkies to keep the labourers calm and several relatives have been able to speak briefly to those trapped. “He said they are safe. He asked us not to worry,” the son of Gabbar Singh Negi, one of the 40 trapped workers, told reporters on Tuesday. While officials said there was enough oxygen getting into the tunnel for the men to survive for five to six days, a doctor on site said several men had started to complain of worrying symptoms, including dizziness, fever and vomiting. Dr BS Pokriyal told the Times of India: “People have started falling ill. We have supplied multivitamins, but we could not send an ORS [oral hydration] pouch as it may get stuck inside the only pipe being used to communicate and send across food and water.” The three-mile tunnel was being constructed in the district of Uttarkashi as part of the Char Dham road scheme, a $1.5bn (£1.2bn) flagship project of the prime minister, Narendra Modi, that aims to improve connectivity across Uttarakhand, which is a popular place for Hindu religious pilgrimage. The project has proved controversial, with environmentalists alleging the heavy drilling and construction required to build and expand the roads was causing subsidence, landslides and heavy environmental damage in the vulnerable Himalayan region. The Uttarakhand government has formed an expert committee to investigate the tunnel disaster.