The death toll in a coal mine explosion rose to five as three more miners died after receiving medical treatment on Saturday in northwest China's Ningxia Hui Autonomous Region, local authorities said.

The explosion occurred at around 2:30 a.m. at Hongyuan Coal Mine at Shikong Town of Zhongning County. It was believed that 12 miners had been trapped underground, according to the county committee of the Communist Party of China.

Two of seven miners injured in the blast were reported to be in critical condition while five others were described as having non-life threatening injures and were also receiving treatment.

Further, these miners were suffering from carbon monoxide poisoning, said Wang Jun, head of the county's health bureau.

Seven people, including Fan Yuxiang, one of the mining company's contractors, have been detained and the mine's accounts have been frozen, said a spokesman with the county's public security bureau.

The township-owned coal mine had been ordered to suspend operations for a safety overhaul when the accident happened, according to the regional coal mine safety supervision authorities.

An initial investigation showed that the explosion was triggered by burning explosives.

Meantime, the County government has launched a three-day inspection of all mines and promised to suspend the operations of any mines with potential safety hazards.