Beijing on the best of days is one of the world's most polluted cities

Air quality in Beijing improved from "dangerous" to "unhealthy" on a sixth day of thick, grey skies that limited visibility and sent people to hospital with breathing difficulties.

A light snow fell on the Chinese capital in the morning, but official measurements of air quality indicated continued high levels of pollutants in the air. The US embassy, which posts air quality readings on its website, warned of "unhealthy" levels.

Beijing on the best of days is one of the world's most polluted cities, but a lack of wind has blanketed the city in smog since Thursday. The pollution has not only strangled the capital, a city of 20 million people, but also other cities in northern, eastern and central China in what state media has dubbed a "smog girdle."

In rare candidness, state media denounced as the causes of the pollution a blind pursuit of economic growth at the cost of the environment and a failure to implement ecological regulations.

Reaction to smog warnings were also often poor. Most schools in Beijing, for instance, were not informed that students' outdoor activities should be stopped, Xinhua said.

"The lingering smog sends a warning message," the Global Times newspaper wrote in an editorial. "Coal burning, dust and industrial and vehicle emissions are the fundamental causes of the hazardous haze."

The government carries the primary responsibility for resolving the problem but the public should not simply play the bystander, it said. The fight against pollution demands contributions from the entire society, the newspaper advised.