Rescue workers are making cautious progress towards freeing 12 workers trapped for their fourth day in a collapsed section of tunnel at the Da Dang-Da Chomo Hydropower Plant in Lam Dong Province, with the threat of further cave-ins forcing them to dig away debris by hand.

Rescue workers outside the collapsed tunnel.

Efforts are now focussed on digging two rescue tunnels around the debris, one by a team from the Vietnam National Coal and Mineral Industries Group and the other by the army.

The Minister of Construction, Trinh Dinh Dung, said excavation was progressing smoothly, with one tunnel having reached 10 metres of the 30 metres required to reach the 11 men and one woman trapped since the tunnel collapse on December 16. But it was unlikely the tunnel can be completed today (December 19).

Colonel Nguyen Huu Hung, deputy chief of staff of Vietnam People's Army, said his team was encountering problems with the substrata and was worried about triggering further collapses if it moves too quickly.

Another rescue team has bored a hole through to the workers from the rear of the tunnel and was running a pump line through to discharge ground water, which at one stage rose to nearly one and a half metres around the trapped workers before a makeshift pumping operation was able to reduce the water level.

Written messages passed between officials and the trapped workers indicated they were in good spirits and, while cold, are in good health. Food supplies and oxygen are being supplied to the workers, trapped about 500 metres from the entrance of the tunnel after the cave-in, through a series of pipes rescuers managed to drive through the hard rock at the beginning of the rescue operation.

Relatives of the trapped workers have joined some 300 rescue officials and army personnel gathered at the site.