Heating has been supplied to almost 100,000 families that were still shivering in mid-December after falling through the cracks of energy conversion projects, according to the Ministry of Environmental Protection.

To cut concentrations of PM2.5 - hazardous fine particulate matter - Beijing and Tianjin, along with 26 cities in Hebei, Shanxi, Shandong and Henan provinces were urged to use natural gas or electricity for heating this winter.

However, as the heating season began, some people in those areas found their homes and schools freezing, mainly due to gas shortages or incomplete energy conversion projects.

From Dec 15 to 20, inspectors went door-to-door and found some 96,000 families that still had no heat on Dec 15, including in Hebei, where temperatures have dropped as low as -10 C.

Local governments have now managed to ensure that all households in the area have been able to stay warm, either through a greater gas supply, coal-fueled heating or electric heaters, according to the ministry.

Before the inspections began, local authorities had helped 330,000 households keep warm by allocating more gas or providing provisional heating equipment, the ministry said.

It told local authorities in November to "ensure a warm winter" for the public and ordered areas with incomplete conversion projects to use coal or any other available fuel.

Last month, the National Development and Reform Commission, the top economic planner, ordered Beijing to restart coal-fueled generators to reduce natural gas consumption.