BEIJING, Oct. 16 (Xinhua) -- China's national observatory on Tuesday issued a yellow alert for thick fog in some northern, eastern and southwestern regions.

On Tuesday morning, thick fog will be seen in nothern Beijing as well as in provinces of Hebei, Shandong, Hunan, Henan, Guizhou and Sichuan, reducing visibility in some areas to less than 200 meters, the National Meteorological Center said.

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