Beijing woke on the first morning of the New Year covered in thick toxic fog, with a concentration of harmful particles 20 times higher than international standards.

After a long period of pollution in December, the Chinese capital was again smothered Sunday in an acrid grey haze which limited visibility to a few hundred metres.

Luminous signs on top of the skyscrapers seemed to float in the fog, while some tourists wore respiratory masks.

Levels of PM 2.5 -- microscopic particles harmful to human health -- exceeded 500 on Sunday morning, according to US Embassy estimates, vastly above the maximum threshold of 25 recommended by the World Health Organization (WHO) for a 24-hour exposure.

On Sunday the exasperation of people in Beijing overwhelmed social networks.

"Why didn't they trigger the red alert? Because it would be a bad omen for the first day of the year?" wrote a surfer on the Weibo microblogging platform.

"Pollution now has its hukou (residence permit) in Beijing. It's made. It will never leave again," replied another.

Most of China's greenhouse gas emissions come from the burning of coal for electricity and heating, which spikes when demand peaks in winter and is the main cause of smog.

Between December 16-21, Beijing along with some 30 other major cities in northern China was on "red alert", a maximum alarm level triggered when severe pollution is likely to last more than 72 hours.

Across the region, construction sites and schools closed and authorities reduced the number of vehicles allowed on the roads in hopes of reducing the thick haze.

On Friday and Saturday 24 Chinese cities in the north and east were again placed on red alert, according to media reports.

Almost all of the alerts were dropped on Sunday, according to official sites, with the notable exception of various districts of Shijiazhuang, the capital of the highly industrialised province of Hebei, where in mid-December pollution was 40 times the maximum recommended WHO threshold.

The issue is a source of enduring public anger in China, which has seen fast economic growth in recent decades but at the cost of widespread environmental problems.

According to official meteorological predictions, the pollution haze will disperse "progressively" from January 5.

China has set a target of reducing its annual coal capacity by 800 million tonnes, according to a government plan reported Saturday by state media.

Despite the target, Beijing expects total coal output to rise to around 3.9 billion tonnes by 2020, compared to 3.75 billion tonnes in 2015, the official Xinhua news agency said, citing a document from the country's top economic planning body.