Thirteen people have been killed in a coal mine gas explosion in China's central Chongqing region, the official news agency Xinhua said Wednesday.

Nine miners died instantly in Monday's blast while the remains of four others were found later, it said, citing a statement issued by the Chongqing municipality.

Three miners who were in the facility at the time of the accident were rescued, it added.

Xinhua said that six people have been taken into custody in connection with the accident.

China's coal mines have a notoriously poor safety record, which the government has repeatedly pledged to address.

In 2010, 2,433 people died in coal mine accidents in China, according to official statistics -- a rate of more than six workers per day.

Labour rights groups, however, say the actual death toll is likely much higher, partly due to under-reporting of accidents as mine bosses seek to limit their economic losses and avoid punishment.