BEIJING, Nov 29 (Reuters) - China"s thermal coal futures dropped 5.6% on Monday after the state economic planner signalled further regulations for prices of the dirty power-generation fuel. The most-active Zhengzhou thermal coal futures contract, for January delivery , was 819.6 yuan ($128.31) a tonne as of 0147 GMT. It has lost more than 142% from a peak of 1,982 yuan a tonne in mid-October following a slew of government interventions to tame the red-hot prices. The National Development and Reform Commission (NDRC) said on Monday that it has summoned key coal miners for advices on improving coal prices mechanism. "After recent abnormal rise in coal prices, it is time to improve the coal prices mechanism," said the NDRC in a statement, adding that all market participants have reached a consensus on the reasonable range of coal prices. But it did not disclose any details of the price level. The NDRC has organised several meetings with coal miners and distributors, as well as power firms and legal experts since late October, aiming to set a coal prices target. read more Some coal miners at top mining regions, Shanxi, Inner Mongolia and Shaanxi, have caped prices at 900 yuan a tonne for 5,500 kilocalorie under regulators" pressures. Meanwhile, Beijing has instructed ramping up of output and power plants to build up inventory as winter heating season kicked in northern China. Coal storage at power generators across China reached 147 million tonnes last week and may hit an all-time high by the end of November, according to the state planner. read more ($1 = 6.3877 Chinese yuan renminbi) Reporting by Muyu Xu and Shivani Singh; Editing by David Gregorio