BEIJING, May 17 -- China's national observatory on Saturday morning renewed a yellow alert for thick fog in some parts of the country.

From Saturday morning to noon, heavy fog with visibility under 1 km will blanket parts of the East China Sea, the coastal waters off Jiangsu and Zhejiang, as well as the port of Shanghai, according to the National Meteorological Center (NMC).

In some regions of Shandong, Jiangsu, Zhejiang, Anhui and Jiangxi, visibility may be reduced to less than 200 meters, the NMC said.

Drivers have been asked to maintain safe speeds, while airports, freeways and ports have been instructed to take appropriate safety measures.

The center also renewed a blue alert for strong gales expected to sweep parts of Inner Mongolia, Hebei, Beijing, Tianjin and Liaoning from 8 a.m. Saturday to 8 a.m. Sunday, with gusts reaching up to 28.4 meters per second.

China has a four-tier color-coded warning system for severe weather, with red being the most serious, followed by orange, yellow and blue.