BEIJING -- China's national observatory on Thursday renewed the yellow alert for thick fog in some regions of the country.

From Thursday morning to evening, heavy fog is expected to blanket the Bohai Strait, most areas of the Yellow Sea, coastal waters of the Liaodong Peninsula, Shandong Peninsula and Jiangsu, according to the National Meteorological Center.

Visibility in some affected areas will be reduced to less than 1,000 meters, the center said.

Drivers have been asked to observe the safe speed limit, and airports, freeways and ports have been told to 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.