Local governments in Beijing, Tianjin, Hebei, Shanxi, Shandong and Henan were required by the Ministry of Environmental Protection in a "double urgent" letter issued on December 4 that regions which had not finished converting their heating supplies to gas should continue using coal or other fuels.
The letter said "keeping people warm in winter should be the number one principle".
The ministry added that for regions that have converted to natural gas or electric heating, local governments should ensure their supplies and prices remain stable.
Beijing has stepped up its efforts to phase out coal use ahead of this year's deadline for air quality targets, vowing to switch 3 million households in the 28 northern cities to gas or electricity.
But while coal has been banned in villages and communities, many residents have yet to be provided with an alternative.
Meanwhile, the coal ban has led to gas shortages and surging prices since the onset of winter, forcing some cities to halt supplies to factories.
China National Petroleum Corp also warned on December 7 that China could see natural gas shortages if the country was hit by "extreme" weather this winter.
The environmental campaign has helped push demand for gas to new highs, but a lack of storage and transport infrastructure means supply is failing to keep pace, the company said in a research report.
As a result, the government would help energy companies to increase imports of natural gas via cross-border pipelines and liquefied natural gas terminals, commerce ministry spokesman Gao Feng said on the same day.
Gas imports in the first ten months of the year rose 24.9% from the same period of 2016, he said.
According to a Bloomberg report published on December 7, China is on course to overtake South Korea to become the world's second-largest importer of liquefied natural gas, behind Japan. It is already the world's top energy user.
Tankers with a combined capacity of 33.6 million tonnes have visited China this year, just 1.7 million below South Korea's total, the report said.
(Writing by Tammy Yang Editing by Jessie Jia)
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