BEIJING, Jan. 17 (Xinhua) -- China's national observatory on Wednesday continued a yellow alert for heavy fog in some northern and eastern regions.

Thick fog will sweep parts of Shandong, Henan, Anhui, Jiangsu, Hubei, Hunan and Sichuan provinces from Wednesday morning, according to the National Meteorological Center (NMC).

In some of the regions, visibility may be reduced to less than 50 meters.

The center said drivers in affected regions should slow down to safe speeds, 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.