A rescue operation was in ongoing on 17 December after 19 miners were trapped after an explosion in a coal mine in north-eastern China's Heilongjiang province, state media reported. The state broadcaster CCTV showed thick smoke coming out from the mine and fire engines parked in line to join the rescue work.

As of 9.30am local time on Thursday the fire was still burning, blocking rescuers from approaching the trapped miners. The blast happened at about 2.30pm on 16 December in Hegang city, when 52 miners were working underground, CCTV said.

The channel stated that 33 of the miners managed to escape after the accident. Rescue work was still underway but Chinese officials say the high concentration of carbon monoxide in the mine means there's little chance of survival for the workers trapped inside.

"Normal concentration of carbon monoxide (CO) should not go higher than 24ppm (parts per million), and currently the CO concentration is 14,650 ppm, reaching a level that people can suffocate to death with just one breath," said spokesman of the rescue and command office, Zhang Qinxiang.

Although the toll from accidents has fallen, China's coal mines are the deadliest in the world because of poor safety and the rush to feed energy demand from the world's second-largest economy.

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