Levels of the tiny airborne particle PM2.5 reached 860 micrograms per cubic meter on Monday in Changchun, the capital of Jilin province, as a blanket of smog falls over northeast China.

The World Health Organization recommends a maximum of 25 micrograms in a 24-hour period.

In Shenyang, the capital of neighboring Liaoning province, PM2.5 levels reached as high as 1,200 micrograms per cubic meter on Sunday.

Authorities in both cities issued alerts, urging residents to stay indoors and ordering factories to cut output in an effort to cut pollution.

The official Xinhua News Agency called the measures "useless."

"When you go out you feel the air burns your eyes, your throat hurts, so you go buy a mask, but it's not really clear what we should specifically be doing," it quoted one resident in Shenyang as saying.

Dangerous pollution has been linked to premature deaths and disease, including heart attacks, stroke, cancer and other lung diseases.

The pollution that has come alongside China's economic growth is a source of popular discontent with the government.

The pollution is caused by coal-fired heating of homes during the winter, factories and cars.

cw/jil (AFP, AP)