China's drive to transform its economy, which includes reducing the role of energy-intensive industries and paring steel capacity, is driving up coal inventories at key ports as demand across a variety of sectors weakens.

Inventories at Qinhuangdao in Hebei province, the largest coal port in China, exceeded what's widely viewed as the warning line of 8 million metric tons on Feb 6, which was a 10-month high, according to the China Coal Transportation and Distribution Association.

The rising stockpiles indicate that downstream users at steel mills, cement factories and coal-fired power plants are reluctant to purchase fuel because of weak market conditions.