BEIJING, Feb. 2 (Xinhua) -- China's national observatory on Saturday issued a yellow alert for thick fog that will hit various parts of the country.

From Saturday night to Sunday morning, thick fog will sweep Hebei, Shandong, Jiangsu and Anhui provinces, reducing visibility in some areas to less than 500 meters, the National Meteorological Center said.

In some regions, visibility may be reduced to less than 200 meters.

The center said drivers in affected regions should slow down, while airports, freeways and ports should take appropriate safety measures.

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