"In the early morning of 27 Dec, there was a suspected poisoning incident at the Qingping Technology Corporation Limited in Yungang district in Datong. Three people died, another six were hospitalised and 28 others were placed under medical supervision", the government of Datong said in a statement.
According to the statement, the scene of the incident was sealed off and the case was under investigation.
The incident comes a week after the founder of a Chinese gaming company died of suspected poisoning. The local police detained one of his colleagues as the primary suspect.
Earlier this month, at least 18 coal miners at a mine in Yongchuan, in southwest China's Chongqing, were killed by carbon monoxide poisoning.