Beijing (Reuters): China 's meteorological authority continues to issue a yellow alert for extreme weather and air pollution Saturday morning.

Dense fog and haze has shrouded the country's central, northern and eastern regions for days.

According to the Central Meteorological Center, heavy fog will sweep across parts of Heibei, Tianjin, Henan, Shanxi, Shandong, Zhejiang and Guangxi from Saturday morning to noon, with the visibility in some areas of Hebei, Henan and Zhejiang being less than 500 meters.

Besides, parts of Beijing, Tianjin, Hebei, Henan, Shandong, Shanxi and Sichuan are also expected to be enveloped by moderate to heavy haze from Saturday to Sunday morning.

China uses a three-tier warning system for extreme weather and air pollution , with red being the most serious, followed by orange and yellow.