The Beijing city government has ordered an immediate restart to coal-fueled generators to ease the shortage of liquefied natural gas in northern China.

In a notice released on Thursday but only widely publicized on Saturday, the capital's City Management Commission confirmed that the National Development and Reform Commission, the top economic planner, had ordered a restart of coal-fueled generators to reduce LNG consumption, Caixin magazine reported.

Three major power plants in Beijing confirmed that they had received the notice, Caixin reported.

To cut concentrations of PM2.5－hazardous fine particulate matter with a diameter of 2.5 microns or less－28 cities including Beijing, Tianjin and cities in Hebei, Shanxi, Shandong and Henan provinces were to use electricity or gas for heating this winter, instead of coal, which is considered the main cause of the lingering winter smog.

However, as the heating season began, some people in these areas found their homes and schools freezing, mainly due to LNG shortages.

The Ministry of Environmental Protection has told authorities to "ensure a warm winter" for the public rather than delay heating supplies in some northern areas due to natural gas shortages or unfinished projects.

Areas that have not yet completed conversion projects to replace coal with gas or electric heating can use coal or any other available measures, the ministry said in a circular released on Thursday.

The China Huaneng power plant in eastern Beijing had restarted one of its coal-fueled generators as of Friday night, with another ready for restart at any time.

Another two plants could also go into service if necessary, the source said.

In 2013, the capital began a gradual process to replace coal-fueled generators with equipment powered by natural gas. The city achieved its coal-free target in March this year.

The old generators at the Huaneng plant were held in reserve in case they were needed.

According to the commission's website, one of the coal-fired generators was used over the summer to cope with a spike in electricity usage for air conditioners during a heat wave.