Authorities say an explosion that killed 28 coal miners in southwest China was caused by a lack of ventilation that caused deadly gases to accumulate.
A state media report on Monday pointed to continuing problems with supervision in the country's mining industry.
China's mines are among the world's deadliest because of lax regulation, corruption and poor operating procedures.
The blast on Saturday afternoon at Sichuan province's Yaozigou mine came less than 24 hours after an explosion in another coal mine in neighbouring Guizhou province killed 12 people.
The official China News Service cited officials as saying that work at Yaozigou was supposed to have been suspended while the mine underwent a technical upgrade that made it temporarily impossible to disperse flammable gases.
A total of 108 miners were working underground at the time of the deadly blast. Eighteen were reported injured, eight of them seriously.
Regulation has been tightened in recent years, but accidents are common because safety is often neglected by managers seeking easy profits.
Official figures show 1,973 people died in coal mining accidents in China in 2011, a 19 per cent fall on the previous year.
Labour rights groups, however, say the actual death toll is likely to be much higher, partly due to under-reporting of accidents as owners seek to limit their economic losses and avoid punishment.
China is the world's biggest consumer of coal, relying on the fossil fuel for 70 per cent of its growing energy needs.