Readings of the PM 2.5 levels of the US Embassy pollution index shoed 248.0 yesterday which is stated to be very unhealthy.

The index dropped to 219 today but still remained very unhealthy category.

China's weather observatory issued yellow alert for smog in Beijing and neighbouring regions in norther parts of the country.

Beijing, Tianjin and parts of Hebei, Liaoning and Shandong provinces will be shrouded by smog from Monday to Tuesday, the National Meteorological Centre (NMC) forecast.

The NMC warns people in the affected areas to reduce outdoor activities.

The smog coincides with the week-long National Day holiday, and many tourists are vacationing in Beijing.

Beijing authorities also issued a yellow alert for smog last evening, the first warning of serious air pollution in the fall this year.

A spokesman with Beijing Municipal Environmental Monitoring Centre said weak winds and humid air have made pollutants hard to disperse.

In addition, satellite monitoring results showed that mass pollution was caused by intense straw burning on the North China Plain.

According to the city's contingency plan for serious air pollution, under the yellow alert, dust control on construction sites should be enhanced and some operation, such as dismantling of buildings, should stop.

It is predicted that air quality in the Chinese capital would improve from Wednesday night, state-run Xinhua news agency reported.

After experiencing frequent bouts of smog, the Chinese public have become increasingly sensitive to the health hazard.

To address public concerns, the government aims to cut the density of inhalable particulate matter by at least 10 per cent in major cities by 2017.