China's top economic planning agency repeated its order on Wednesday for coal companies to keep coal prices stable, one week after it made the same call as part of the government's efforts to check inflation.

Coal producers should work to increase production, ensure supplies and keep prices stable, Cao Changqing, head of the Department of Price of the National Development and Reform Commission (NDRC), said at a conference in Taiyuan, capital of coal-rich Shanxi province.

The rise of coal prices remarkably outpaced that of prices of downstream products in recent years, adding rising cost pressures to industries, including power, construction materials, fertilizer and metallurgy, he said.

China had solid foundations to stabilize coal prices as supplies increased and demand weakened due to the government's move on energy savings and emission reductions, he said.

He also encouraged large state-owned coal enterprises to sign long-term agreements with power firms. Additionally, coal companies were required to keep prices unchanged for coal excavated under 2011 annual supply contracts, compared to 2010.

On Nov. 22, the NDRC asked coal producers to boost self-discipline and required local governments not to restrict sales of coal outside their provinces to ensure price stability.

China has stepped up measures to contain prices in November after the consumer price index (CPI) rose 4.4 percent during the 12 months through October to a 25-month high.