BEIJING, July 30 (Reuters) - China will encourage qualified coal mines to expand production capacity, the country's state planner said on Friday, in an effort to boost coal supply and cool prices of the commodity.

Coal miners, who apply for capacity expansion before March 31, 2022 must promise to shut down a certain amount of outdated production capacity and complete the closure within three months after receiving the approvals, it said in a statement. (Reporting by Muyu Xu and Dominique Patton)