LUCKNOW, India (AP) — Some of the 40 construction workers trapped in a collapsed road tunnel for a fourth day were getting sick as falling debris and technical glitches delayed the work to free them, officials in northern India said Wednesday.

Rescuers have been trying to drill wide pipes through excavated rubble to create a passage to free the workers trapped since Sunday after a portion of the under-construction road collapsed in mountainous Uttarakhand state. But the government-run national highway authority said that the process was slower than expected and that another high-power drilling machine was being airlifted from New Delhi to be used as soon as possible.

The authority also said the workers “confirmed the receipt of food items” and that all of them were safe “as communicated by them.”

Relatives and friends of the trapped workers, gathered outside the tunnel, were growing frustrated and angry.

Most of the workers are migrant labourers from across India.

Magistrate Abhishek Ruhela said some workers had sent messages that they were suffering from fever, body aches, and were getting worried. Medicine has been sent through pipes that were set up earlier to get water and food to the workers.

“Essential edibles such as chickpeas and almonds are being sent through the same channels,” Ruhela said.

About 200 disaster relief personnel have been using drilling equipment and excavators in the rescue operation with the plan to push steel pipes 2.5-foot (0.76 metre) -wide through an opening of excavated debris with the help of hydraulic jacks to safely pull out the stranded workers.

Falling debris also delayed the start of the drilling on Tuesday. “These are challenges in such rescue operations, but we will overcome them,” Ranjit Sinha, a disaster management official, said.

Two of the rescuers were reported to have minor injuries because of debris.

A landslide Sunday caused a portion of the 4.5-kilometer (2.7-mile) tunnel to collapse about 200 metres (500 feet) from the entrance. It is a hilly tract of land, prone to landslide and subsidence.

Uttarakhand is a mountainous state dotted with Hindu temples that attract many pilgrims and tourists and construction of highways and buildings has been constant to accommodate the influx. The tunnel is part of the busy Chardham all-weather road, a flagship federal project connecting various Hindu pilgrimage sites.