China will reduce the discharge of pollutants by 60 percent before 2020 through a major upgrade of its coal-fired power plants, officials said Wednesday, as major climate talks were underway in Paris.

The move will save around 100 million tonnes of raw coal and cut carbon dioxide emissions by 180 million tonnes annually, the official Xinhua news agency quoted the State Council, or cabinet, as saying.

By 2020 China will have shut down plants that do not meet the energy-saving standard, according to a statement from the council -- which came a day after Beijing was blanketed in choking smog.

China is the world's biggest polluter, and its emissions of the greenhouse gases that cause climate change -- along with its ability to fulfil its promises -- are due to be a central issue at the Paris climate summit.

However, the saving of carbon dioxide emissions by 180 million tonnes annually is a fraction of the Asian giant's total emissions of the greenhouse gas, estimated to have reached nine to ten billion tonnes in 2013.

Likewise, the 100 million tonnes reduction of raw coal consumption is only a small proportion of China's annual coal use, which hit 4.2 billion tonnes in 2013.

- Choking smog -

Greenpeace welcomed the move from Beijing, but said the commitments had already been released, although they had not been widely publicised.

"It's not well known. It's embedded already in the policy. It's probably not been framed that way before. They chose to frame it a little more explicitly," Li Shou, Greenpeace China's climate and energy campaigner, told AFP.

"The background is Beijing had a very bad round of air pollution in these past two or three days."

Beijing ordered hundreds of factories to shut and allowed children to skip school on Tuesday as choking smog reached over 25 times safe levels.

The pollution has become a key cause of public discontent with the ruling Communist party.

"China has put in place new air pollutant emission standards for coal-fired power plants that are in some respects stricter than the corresponding standards in the EU, and has been installing emission controls at an astonishing pace," Li said.

Li added that power generation from coal will fall in the future, saying: "As China at the same time achieves the goal of reducing the CO2 emissions per unit of coal-fired power generated, the fall in power sector CO2 emissions will be much more than 180Mt."

China intends to reduce coal's share of its total energy needs to below 65 percent by 2017, Xinhua reported, down from approximately 70 per cent currently.

China has also pledged to curb greenhouse gas emissions, most of which come from coal burning which spikes in winter along with demand for heating.

At the climate change summit in Paris this week, President Xi Jinping repeated China's pledge that emissions would peak by "around 2030".

China is estimated to have emitted nearly twice as much carbon dioxide as the United States in 2013, and around two and a half times the European Union's total.