BEIJING (Reuters) - China's state planner has issued an order to ensure stable supplies of coal, oil and gas, state news agency Xinhua said on Sunday, as the country heads into the winter amid a coal supply crunch. The National Development and Reform Commission said it will ensure a rational level of stockpiles to guarantee stable supplies at key times and in key areas for power generation, Xinhua said. There must be a focus put on resolving problems and difficulties in important regions, and efforts put into ensuring coal supplies for winter heating, it added. China's northeastern industrial heartland may face winter power and heating cuts after authorities in Beijing spurned requests from provincial providers for help securing coal supplies after two major mines were forced to halt output, utilities warned last month. The mine halt is part of concerted efforts by China to tame increasingly severe winter smog in industrial centres, especially in northern China where temperatures plummet over the winter months. (Reporting by Ben Blanchard)