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Rescuers are preparing a special capsule to winch to safety four miners who have been trapped 220m under ground since Christmas Day
The men have survived on food and water sent through an emergency hole since the collapse of the mine in China’s Shandong province.
The collapse was so big it was picked up on equipment designed to detect earthquakes.
Twenty-nine miners were originally trapped - 11 have escaped or been rescued, one is confirmed dead and 13 are still missing without trace.
Infrared cameras were sent down and found the survivors waving their hands in the darkness to attract attention.
Rescuers have now drilled down to within around 40m of the remaining four, but the process has been slow going because of the need to constantly check the ground is secure.
When the hole is complete the slender metal capsule - around 50cm across - will be lowered down to winch them out one by one.
The rescue pod has a built-in pulley system to minimise any friction against the wall of the escape shaft.
Andreas Hafner, from Bauer Equipment Shanghai, said the drilling at the gypsum mine was still a very delicate procedure.
"We have to continuously see what are the soil layers, and we hope with these drilling methods we do not need to change anymore, and we keep going quite fast to rescue the people," he said.
Rescuers have already experienced problems - a drill got stuck in a gypsum layer 170m down on 9 January and days later the wall of one of the rescue holes collapsed.
The chief executive of Yurong Trade Company, the owner of the mine, apparently took his own life days after the collapse by jumping into a mine well as he was helping with the rescue effort.
China has a history of fatal mine accidents, with 931 killed last year, but that figure is significantly down on 2002 when nearly 7,000 deaths were reported.