BEIJING/JINAN, Nov. 26 (Xinhua) -- Heavy fog hit many parts of east and north China on Monday, forcing several highways to shut down.

With visibility reduced to less than 200 meters in many places in east China's Shandong Province, dozens of toll stations on more than ten highways closed or restricted the number of vehicles as of Monday morning.

The Shandong provincial meteorological bureau upgraded the alert for heavy fog on Monday morning from yellow to orange, the second highest in the three-level alert system.

In Beijing, a total of eight highways were closed Monday morning due to low visibility caused by heavy fog and smog, according to the Beijing traffic control department.

At around 9 a.m., the density of air pollution indicators PM2.5 and PM10 stayed at 225 micrograms per cubic meter and 129 micrograms per cubic meter respectively.

Most parts of Beijing suffered from heavy air pollution, according to the Beijing environmental protection monitoring center. It forecasted that a sandstorm is approaching Beijing from the northwestern region.

China's national observatory on Monday renewed an orange alert for thick fog in some northern, eastern and southwestern regions.

From Monday to Tuesday, thick fog will be seen in the provinces of Jiangsu, Anhui, Shandong, Hebei, and Sichuan, reducing visibility in some areas to less than 50 meters, the National Meteorological Center said.

The center said drivers in affected regions should slow down, while airports, freeways and ports should 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.?