Xinhua said managers of the Rui Zhiyuan coal mine in Shanxi province's Hongtong county had delayed reporting the accident overnight, wasting the crucial hours when co-ordinated rescue efforts could be most effective.
Xinhua said rescuer workers believed the mine's managers delayed reporting the accident "as they were trying to launch rescue operation by themselves, which magnified the number of casualties."
The state work safety administration said the mine was properly licensed, was owned by the local government and had an annual output capacity of 210,000 tonnes of coal.
It said the mine's managers were being questioned by police and that its bank account had been frozen.
China's coal mining industry is the most dangerous in the world, averaging 13 deaths a day from fires, explosions and floods. In August, 181 miners died when rains flooded two mines in Shandong province.
Many of the accidents are blamed on mine owners who disregard safety rules and fail to invest in ventilation and fire control equipment.
Meanwhile, 11 people were trapped after a roof collapsed in an iron and gold mine in Chengde in Hebei province, in northern China, Xinhua said.
Xinhua reported separately that 12 people died of gas poisoning in the Xinjiang region in an outdoor tent that was being used by workers who were digging for licorice root, a medicinal herb used in traditional Chinese medicine.