Geothermal energy could be about to play a much larger role in heating the heavily-polluted cities clustered in northern China that have traditionally been major consumers of coal and massive victims of winter smog, an industry insider said.

"We need to fully utilize geothermal energy, a renewable clean energy buried underground, to replace coal as winter heating fuel," said Huang Gang, head of Huabei Oilfield Co, which is headquartered in Cangzhou, Hebei province. "It could alleviate the severe smog in the Beijing-Tianjin-Hebei region."

The company is a branch of domestic energy giant China National Petroleum Corp.

Geothermal energy is stored thermal energy produced naturally within the Earth's crust and stored underground.

It was created during the original formation of the planet and also comes from radioactive decay.

Hebei has been hit by smog in recent years and at least six of its cities have languished in the bottom 10 for air quality since 2013.

Massive coal consumption, especially within rural villages where it is widely used for heating, has been the major cause of that winter smog, said the Ministry of Environmental Protection, which suggested the region reduces its reliance on fossil fuels.

Total energy consumption in the Beijing-Tianjin-Hebei region hit the equivalent of 456 metric million tons of coal in 2015. While some other forms of energy contributed to this total, 90 percent of the power came from coal.

A survey conducted by the China Geological Survey under the Ministry of Land and Resources that was released in February said coal consumption spewed out huge amounts of sulfur dioxide, with 80.8 percent of the total amount of sulfur dioxide coming from energy consumption.

"Geothermal resources discovered during the process of extracting oil have been utilized to generate electricity and they have worked well during the past four years," said Huang, who added that his company had invested 100 million yuan ($15.4 million) on exploiting buried geothermal resources.

The survey said geothermal resources are rich in the Beijing-Tianjin-Hebei area and could contribute 87 percent of regional energy consumption.

It added that, if the resources are fully utilized, the region could reduce the emission of carbon dioxide by 818 million tons annually, a major step in improving air pollution.

"But currently, this renewable resource has failed to play its role in air quality improvement because of its limited use," said Huang, who added that some governments and companies have explored geothermal resources as an option in providing heat for homes and greenhouses.

Huang said major investment would be needed to fully exploit geothermal energy sources for the generation of power and heat, which would require policies to encourage and regulate participation from the private sector.

He said there are currently few such preferential policies.

Technical development in the exploration of geothermal resources is currently insufficient and developers must focus on the sustainable use of the resources by recharging water back underground to promote environmental protection, he added.

"In the pursuit of cleaner air, we must promote the use of geothermal resources along with a scientific exploration plan that guarantees its sustainable use," he said.

Zhang Laibin, the head of China University of Petroleum, said the central government should take the lead in mapping the concentrated locations of geothermal resources in the country to offer a full and clear picture of the potential and that it should also introduce the basic mechanisms to oversee sustainable exploration.