Tourists gather in Tiananmen Square in Beijing, Oct 1, 2016. [Photo/IC]

BEIJING -- Beijing issued its first yellow alert for air pollution in the second half of this year, forecasting that smog will continue through Monday.

The alert means restrictions on work at construction sites, no outdoor barbecues or straw burning of farmers.

The reading of Air Quality Index (AQI) in Beijing was between 200 and 300, meaning heavy pollution, on Saturday.

The smog began to envelop the capital and surrounding areas on Saturday, just as a week of national holidays began.

The National Meteorological Center issued a yellow alert for smog on Sunday.

The smog will be dispersed by a cold snap on Tuesday.

Wang Zifa, a researcher with the Institute of Atmospheric Physics of the Chinese Academy of Sciences, expects north China to face more bouts of smog in autumn and winter this year.

China has a four-tier color-coded system for severe weather, with red being the most serious, followed by orange, yellow and blue.