Twenty-one miners were hospitalised and up to 20 more were still trapped at the accident site in Xingtai county of Hebei province, the Xinhua news agency said.
Rescuers working frantically through tonnes of mud and stone were encouraged by faint signs of life.
None of the three mines had obtained safety certificates from the authorities, and all had been operating despite an order to cease work for the time being, the national work safety administration said in a statement.