Rescuers had recovered 21 bodies from the site of a mining accident in north China's Shanxi Province as of Monday, the end of a three day search operation, Xinhua reported. An initial investigation found 34 miners were working underground on Saturday when the accident took place at about 11:20 a.m. at Wujiu Coal Mine in Nanjiao District, Datong City. Thirteen survived but others were fatally poisoned by carbon monoxide, according to a Datong City official. The owner of the mine was detained by police. Poor management of the mine had made it difficult to determine the number of workers underground at the time of the incident. The government did not exclude the possibility the death toll may increase. A preliminary investigation showed a gas blast or spontaneous ignition were the likely causes of the accident. More than 100 people participated in the search and rescue operation. The coal mine was registered with an annual production capacity of 150,000 tons. Datong, in the north of the coal-rich province, has been called China's "capital of coal."