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

The National Meteorological Center has forecast that heavy fog will cover parts of Hebei, Shanxi, Jiangxi, Zhejiang, Fujian and Guangdong from Tuesday evening to Wednesday morning.

Visibility is expected to be reduced to under 200 meters in some affected areas, the center said.

It has advised motorists to control their speed to ensure safety in heavy fog conditions, and said that precautionary measures should be taken at airports, on expressways and at ferry terminals to promote safe travel.

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