Thirteen people were killed and another 20 missing after an explosion in a coal mine occurred in China's Chongqing, state media reported.

As of midnight, rescuers have found 13 dead bodies, while rescuers are continuing their search operation for the 20 other workers who are believed to be trapped inside, Global Times reported citing Chongqing's deputy mayor Mu Huaping during a press briefing early on Tuesday.

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The officials also corrected previous casualty reports that said 15 miners were confirmed dead, BBC reported. "We are still working all-out to search for the 20 missing miners... and will exert out utmost as long as there's still a ray of hope," the official said.

Over 400 rescue personnel were working overnight, shifting turns on going down the shaft to carry out its search and rescue operation. Global Times noted the rescue team needed to dig through the underground passageways that have been hampered by the ruins from the collapsed tunnels.

Also, there are at least 20 ambulances and several medical workers on standby.

The blast reportedly took place at 11:30 a.m. on Monday at the Jinshangou Coal Mine in the town of Laisu. There were 35 miners working when the accident occurred, and only two were rescued on Monday.

After the accident, Chongqing officials have implemented a strict safety overhaul, temporarily closing down all collieries with less than 90,000 tons of yearly output. The Jinshangou mine has a 60,000 annual output, based on its license.

Meanwhile, the State Administration of Work Safety has also launched an investigation into the blast, "adding that those responsible must be strictly punished," the Aljazeera reported.

TagsGas Explosion, coal mine explosion, explosion accidents, Chongqing explosion