Most accidents are caused by a failure to follow safety rules, including a lack of required ventilation or fire control equipment.

However, recent efforts by the government to crack down on mine safety - including the closure of many small, dangerous mines - appear to be having some effect.

According to official reports the average number of miners killed so far this year has been halved to around six a day.

Nonetheless labour rights groups say the real death toll may be far higher, with many accidents covered up or unreported by mine owners working in collusion with local officials.