It will take at least 15 more days to get through a massive amount of debris and reach miners already trapped for 11 days since an explosion in a gold mine in eastern China, authorities said.
The mine shaft is blocked 350 metres (1,000ft) below the surface by 70 tons of debris that extends down another 100 metres (330ft), the Yantai city government said in a statement on its social media account.
“Based on expert evaluations, the extent of the blockage … is well out of expectation,” the statement said.
One worker has died from head injuries in the explosion, state media said earlier.
Of the remaining 21, rescuers have established contact with 11 and the status of the other 10 is unknown.
The deceased worker had been in a coma.
Two others are said to be in poor health.
Rescuers have delivered food, medicine and other supplies to the group of 11 as they work to remove debris and improve ventilation.
The state media reports said exhaustion has set in among some of the workers since the January 10 explosion ripped through the mine that was under construction in Qixia, a jurisdiction under Yantai in Shandong province.
Rescuers were attempting to clear cages and other debris blocking the main shaft while drilling other shafts for communication, ventilation and possibly to lift workers to the surface.
Boring has reached depths of around 700 metres (about 2,000ft), the reports said.
Mine managers have been detained for waiting more than 24 hours before reporting the accident, the cause of which has not been announced.
Increased supervision has improved safety in China’s mining industry, which used to average 5,000 deaths per year.
Yet demand for coal and precious metals continues to prompt corner-cutting, and two accidents in Chongqing last year killed 39 miners.