Pollution in Beijing- Three day "red" alert" has been declared by the administration

Heavy smog descended upon the Chinese capital this week as Beijing issued its first three day pollution 'red alert'.

The unprecedented move followed scathing public criticism aimed at the city's weak response to last week's thick haze, which saw pollution skyrocket to record levels. The key cause of smog is the burning of coal (for electricity and heating), which also contributes the the country's greenhouse gas emissions.

Beijing put its air pollution emergency plan into action on Monday, pulling half of all private vehicles off the streets, ordering many factories to close and recommending that some schools allow students to remain at home. The use of conventional petrol-powered and hybrid cars was limited to alternate days, an unprecedented boon for China's nascent electric car market.

The recurrent bad air drove residents to hospitals in growing numbers, and pollution mask sales soared by as much as 400 per cent. Meanwhile, Chinese e-commerce giant Alibaba was overrun for searches for air purifiers and masks.

The chronic haze blanketing northeastern China earlier this month was so thick that, unlike the Great Wall, it could be seen from outer space, according to satellite photographs from NASA.

One traveller on a high-speed train from the capital to the central province of Hubei posted said, “Every city in north China that I passed was covered by smog and looked like a dead town.”

People walking in the central business district on clear and polluted days in Beijing. Beijing's first ever red alert for smog expired on Thursday as blue skies and sunshine replaced the thick haze that covered the city for days. –AFP

A policeman wearing a mask stands guard in front of the giant portrait of Chinese late chairman Mao Zedong, amid heavy smog. –Reuters

A electric screen showing Shanghai Pudong financial area in a clear day is seen amid heavy smog in Zhengzhou, Henan province on Wednesday. –Reuters

A Roewe E50 electric car is parked next to a street as a bicycle travels past, amid heavy smog on Wednesday. The use of conventional petrol-powered and hybrid cars was limited to alternate days, an unprecedent boon for China's nascent electric car market. –Reuters

This combo image of two photographs taken on December 10, 2015 (left) and two days earlier on December 8 (right) shows men looking at the view on clear and cloudy days over Beijing. –AFP

Women pass by clothes hanging outside in an area next to a coal power plant in Beijing during a smog-free and also the last day of the city's first "red alert" for air pollution. –Reuters

This combination image of two photographs taken on December 10, 2015 (right) and the previous day on December 9 (left) shows a cyclist and pedestrian on clear and polluted days in Beijing. –AFP

A migrant worker steps out of his accommodation in an area next to a coal power plant in Beijing. The key cause of smog is the burning of coal (for electricity and heating), which also contributes the the country's greenhouse gas emissions. –Reuters

Women work in their home in an area next to a coal power plant in Beijing during a smog-free and also the last day of the city's first "red alert" for air pollution on Thursday. –Reuters

Visitors look at the view over the Forbidden City from the top of Jingshan park on a clear day, as the city's red alert for smog expires. –AFP

A man looks out at the view over the city from the top of Jingshan park on a clear day in Beijing on Thursday. –AFP

Visitors walk out of the gate of the Forbidden City in Beijing on Thursday, when Beijing's first ever red alert for smog expired, giving way to blue skies and sunshine. –AFP