Photo taken on Oct. 30, 2011 shows the city is enveloped by heavy fog in Beijing, capital of China. Heavy fog shrouds several northern and eastern Chinese regions Sunday. (Photo: Xinhua)

Thick fog continued to blanket China's northern and eastern regions on Monday morning, the National Meteorological Center said, warning of increased safety risks on roads and docks, as well as at airports.

The country's top meteorological authority issued a yellow alert, the second in a four-scale alert system, at 6 a.m, urging people in fog-affected areas to be aware of the air quality which will be worsened by the fog and to reduce driving speeds to ensure safety.

Fog and haze will decrease visibility to within 1,000 meters in some parts of Beijing, Tianjin, Liaoning, Hebei, Henan, Shanxi, Shandong, Anhui, Hunan, Hubei, Zhejiang and Jiangsu, and as low as 200 meters in some areas, the center said.

In northeast China's Liaoning Province, 41 toll gates on provincial expressways were closed Monday morning, said officials with the provincial transportation department.

The city of Dalian in southern Liaoning has been worst hit by the fog and a red alert, the highest in the four-scale alert system, was issued by the Shenyang Meteorological Center, as visibility was reduced to less than 50 meters in the city of Pulandian and Jinzhou district, officials said.

The fog will disperse on Tuesday as rains move into north China, the national meteorological center said.