The open-pit mine operated by small local firm Xinjing Coal Mining Co collapsed on Wednesday in a landslide, leaving dozens of workers buried under a huge pile of debris 500 metres wide and an estimated 80 metres high, according to state broadcaster CCTV.
Dramatic security camera footage aired on CCTV on Thursday showed an avalanche of rock and soil falling from one side of the mountain into the mine pit, burying a number of excavators and dump trucks.
Three hundred rescue workers were at the site using heavy machinery and rescue dogs to aid in their search for the trapped miners, state media said.
The National Health Commission said on Wednesday evening that six injured people had been rescued from the mine.
"I had just started work at 1.15 in the afternoon when I realised that rocks were falling from the mountain," a hospitalised miner told CCTV on Thursday.
"I saw that the situation was getting more and more serious, and an evacuation was organised, but it was too late, the mountain just collapsed."
Coal is a major source of energy in China but its mines are among the world's deadliest, largely due to lax enforcement of safety standards, despite repeated government orders for improvements in safety over the years.
President Xi Jinping on Wednesday ordered search and rescue efforts, state media reported, although a second landslide in the evening hampered the work to find survivors.
"We must make every possible effort to rescue the missing persons and treat the injured," Xi said.
Premier Li Keqiang also demanded a quick investigation into the cause of the collapse.
Local governments in several regions, including Inner Mongolia, Shanxi and Shaanxi, have ordered coal miners, especially open-pit mines, to immediately conduct safety checks and local authorities to carry out inspections following the collapse.
China's mines have been trying to boost output over the past year under a government call for greater supplies and stable prices. The government is estimated to have approved 260 million tonnes of new coal mining capacity in 2022. Inner Mongolia is the country's top coal-producing region.
The mine near the town of Alxa League was previously an underground mine. It was converted into an open-pit operation in 2012, according to state media. It had suspended production for three years before restarting in April 2021, state media added, though it did not provide further information regarding the cause of the closure.Â
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