As northern China continued on Monday to choke under a vast cloud of toxic smog, factories and schools remained closed and the number of cars on roads was limited. A "red alert" was issued from Friday night to Wednesday in at least 23 cities, marking the first time the measure has been taken this year in Beijing, which is home to 22 million people.

According to state media, more than 700 companies stopped production in the capital. Authorities in northern Hebei province ordered coal and cement plants to temporarily shut down or reduce production.

In other areas, hospitals prepared teams of doctors to handle an expected surge in cases of pollution-related illnesses.

'Worst yet to come'

According to data maintained by the US Embassy, Beijing's air quality on Monday morning was better than feared, with PM 2.5 levels hovering around 200.

However, the figure remained eight times the World Health Organization's daily recommended maximum exposure level to the microscopic particles - measuring 2.5 microns across - which carry major health risks.

Beijing's meteorological authority also told AFP news agency that the relatively low number was just a temporary reprieve, warning that the worst haze would hit the city on Monday night and linger until Tuesday.

Economy vs. environment

In neighboring Shijiazhuang, the capital of Hebei province, PM 2.5 levels stood as high as 701 at noon, with levels of larger PM 10 particles even higher.

China's long-standing air pollution is blamed on car emissions as well as its reliance on coal for electricity and heating, which spikes when demand peaks in winter.

The issue is a source of enduring public anger in China, where fast economic growth in recent decades has come at the cost of environmental and health concerns.

ksb/tj (AFP, AP)