Three workers who were trapped inside a collapsed railway tunnel have been found dead, despite rescue efforts that lasted over five days, Thai authorities announced.

According to the BBC, the men, two from China and one from Myanmar, were believed to be still alive until Thursday, August 29.

The three workers were trapped when part of the tunnel they were constructing collapsed on Saturday, August 30, in the Pak Chong area, about 200 kilometers northeast of Bangkok.

Today, Friday, August 30, the authorities announced that all three had died, with initial investigations indicating that the cause was a lack of air.

The under-construction tunnel, part of the Thailand-China high-speed rail project, collapsed due to a landslide at around 11:40 PM local time (4:40 PM Greece time) last Saturday.

Rescuers, consisting of officials from Thailand’s State Railway (SRT) and a Chinese disaster response team, worked around the clock last week, hoping to save the victims.

They had tried to pump oxygen into the tunnel to keep the workers alive, but it is unclear if the pipes they used reached the workers.

Meanwhile, yesterday, the body of a Burmese truck driver was found buried under a pile of soil and rocks, and at midnight on Wednesday, the bodies of two Chinese workers—a supervisor and an excavator operator—were found about 25 meters from the tunnel collapse site.

The rescue operation was quite difficult, as rescuers built three-meter structures for their safety and had to be careful not to cause further collapse of the tunnel.

The Thai police have launched an investigation into the incident, while construction work around the tunnel has been temporarily suspended.