BEIJING — China's national observatory renewed a yellow alert on May 1 for heavy fog in sea areas and parts of the central and southwestern regions.

Thick fog will affect coastal waters off the Liaodong Peninsula, the Shandong Peninsula and the provinces of Zhejiang and Fujian, as well as parts of the Bohai Strait and the Yellow Sea on May 1, according to the National Meteorological Center (NMC).

Visibility in the affected areas will be reduced to less than 1 km, the NMC said.

The observatory also forecasted heavy fog in parts of the Central Hubei province and the southwestern Chongqing Municipality, reducing the visibility in some of the areas to less than 500 meters.

The NMC said drivers 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.