BEIJING -- China's top observatory on Monday renewed a yellow alert for thick fog in a vast part of central, southern and eastern China.

On Monday morning, thick fog will affect some parts of Shandong, Henan, Jiangsu, Zhejiang, Hunan and Fujian provinces, reducing visibility in some areas to less than 200 meters, the National Meteorological Center said on its website.

The center warned that 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.