Three foreign workers trapped in a collapsed train tunnel in Thailand have died despite a rescue operation that lasted over five days, Thai authorities confirmed. The men, two from China and one from Myanmar, were believed to be alive as late as Thursday.

The collapse occurred last Saturday in Pak Chong district, about 200 km (124 miles) northeast of Bangkok, during the construction of a tunnel that is part of the Thailand-China high-speed railway project. A landslide at approximately 23:40 local time (16:40 GMT) caused the tunnel to give way.

On Friday, authorities reported that all three workers had died, likely due to a lack of air. Rescuers, including officials from the State Railway of Thailand (SRT) and a Chinese disaster response team, worked around the clock in an effort to save the men. They attempted to pump oxygen into the tunnel, but it remains unclear whether the oxygen tubes reached the trapped workers.

On Thursday, rescuers recovered the body of a Burmese truck driver buried under debris. The bodies of the two Chinese workers, a supervisor and an excavator operator, were found early Friday morning around 06:00 local time (00:00 GMT), approximately 25 meters from the collapse site.

Local reports suggested that on Wednesday, rescuers came within a meter of one of the men and even detected faint sounds, raising hopes that the workers were still alive. Scanners and sniffer dogs had also detected vital signs. However, rescue progress was hampered by the ongoing landslide, with falling dirt repeatedly blocking the rescue paths into the tunnel.

Thailand’s caretaker Interior Minister, Anutin Charnvirakul, stated that the rescue efforts were complicated by “the limitation of engineering.” He emphasized the need for caution to avoid triggering further collapses and noted that rescuers had to construct 3-meter (9.8 ft) high support structures to ensure their own safety during the operation.

“No one wanted this incident to happen,” Charnvirakul said during a press conference on Friday. “We tried not only to save the victims’ lives but also to ensure the safety of the rescuers and workers.”

The bodies of the three men were retrieved from the tunnel on Friday. Thai police have launched an investigation into the incident, and construction activities around the tunnel have been suspended pending further review.