The index was also 1.21 percent lower than that of the same period a year ago.
Despite robust daily consumption, coal stockpiles remained at a high level. On Wednesday, six major coastal power plants saw a total of 16.92 million tonnes of coal inventory, up nearly 6 million tonnes year on year.
Analysts also pointed to growing bearish sentiments on coal prices and a gloomy global market.
The country is in the middle of capacity cutting in its overloaded coal sectors, with plans to reduce a further 150 million tonnes of capacity this year.