HARBIN — Five people were killed in a coal mine accident in northeast China's Heilongjiang province, company sources said.

The accident happened on Monday night at the Xing'an coal mine of the Hegang mining company under the Heilongjiang Longmay Group, trapping nine people. Four of them were rescued, according to the mining company.

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A preliminary investigation showed that it was caused by the leakage of liquid carbon dioxide.

Further investigation into the cause of the accident is underway.