BEIJING, Jan. 2 -- China's national observatory on Tuesday renewed a yellow alert for thick fog in some parts of the country.

On Tuesday morning, heavy fog is expected to affect parts of Beijing, Tianjin, Hebei, Shandong, Jiangsu, Anhui, Sichuan Basin, Fujian, Liaoning and Xinjiang, according to the National Meteorological Center.

Visibility in some affected areas will be reduced to less than 200 meters and even below 50 meters, the center said.

Motorists are advised to control their speed to ensure safety, while precautionary measures should be taken at airports, on expressways and at ferry terminals to ensure traffic safety, according to the center.

China has a three-tier color-coded warning system for thick fog, with red being the most serious, followed by orange and yellow.