The number of casualties has now risen to 32, the Xinhua news agency reported.
The incident took place at a mine belonging to the Baoma Mining company in the city of Chifeng. Earlier, local officials said four miners had been rescued and search operations continued.
An investigation has reportedly been launched into the incident, which was attributed to a gas leak. Over 180 people were working underground at the time of the blast, with at least 149 escaping to the surface.