More than 1.3 million people have fallen sick in the kingdom since the start of the year as a result of air pollution, with nearly 200,000 admitted to hospital this week alone.

The Indian capital's pollution causes illnesses such as asthma and other respiratory problems every winter as the heavy air does not let vehicular emissions, construction dust and farm-fire residues disperse easily.

Daily coal production in Jharia this year jumped to 100,000 tonnes, up from an average of 80,000 tonnes until 2021, local mining officials say.

The national capital Delhi and surrounding areas are enveloped in a layer of smog each winter as cold, heavy air traps construction dust, vehicle emissions and smoke from the crop stubble burning.

The decision to shut some schools came after concerned parents and environmentalists took to social media, urging the authorities to consider the impact of pollution on children.

The world's most polluted capital is blanketed in smog every winter as cold, heavy air traps construction dust, vehicle emissions and smoke from the burning of crop stubble to clear the fields for the next crop.

High pollution is an annual sore point for Delhi, when several people are put to risk due to a high concentration of tiny airborne particles, especially in October and November.

State agencies have pumped thousands of dollars into Shellios Technolabs, a startup whose founder Amit Pathak began work on the helmet, which he calls the world's first of its kind, in a basement in 2016.

Nearly 60% of China's economy is powered by coal and the country has seen a surge in imports of the fossil fuel and mining to help combat a power crunch that has crippled factories.

Beijing has improved its air quality since China won its bid to host the Games, but the Ministry of Ecology and Environment says winter smog risks remains 'severe'.

Pollution levels dropped marginally earlier this week, but the Air Quality Index on Thursday touched 393 on a scale of 500, indicating risks of respiratory illness from prolonged exposure.

Delhi's choking air put more children in hospital with breathing problems and the government shut five power stations and extended school closures to contain the crisis.