Spot thermal coal prices at China's top coal port Qinhuangdao remained unchanged from a week earlier, stagnant since the beginning of June, as power use growth slowed and supply remained adequate.

Coal with a calorific value of 5,800 kcal/kg (NAR) was quoted at 780 to 790 yuan ($115.10-$116.50) per tonne, and coal with a calorific value of 5,500 kcal/kg remained at 750 to 760 yuan, according to Qinhuangdao Seaborne Coal Market .

"Coal stocks are high, and hydropower generation has jumped. Coal is not selling as well as in past summers," said a Beijing-based trader, "Spot traders are standing on the sidelines of the market as outlook is quite murky."

China's power generation in June grew 11.4 percent on the year, the slowest growth in a non-holiday month since last October. Thermal power generation increased 8.6 percent, compared with a 18.5 percent jump in hydropower output.

"Chinese power production growth is slowing in line with the economy, but not at a particularly alarming rate," said a Macquarie research note. "We would expect the rate of improvement in hydro to slow in coming months and thermal power to pick up some of the more modest gains in 2H10. This should be enough to ensure appetite for imports will be solid, albeit at lower rates than seen earlier in the year."

The latest data showed that coal stocks at major power plants were at a comfortable level at 18 days of consumption as of July 7, according to data published by Zhongneng Power Industry Fuel Co and published on sxcoal.com.

Coal stockpiles at Qinhuangdao increased 2 percent from a week earlier to 5.9 million tonnes by July 19, port data showed.