- China's white bullet train turned brown while passing pollution-hit areas
- The country's observatory renewed alerts for air pollution and fog
- Many Chinese cities have suffered from frequent winter smog recently
The national observatory renewed alerts for air pollution and fog for some areas in northern, eastern and central China, including Beijing.
Heavy smog will persist in parts of Beijing, Tianjin, Hebei, Henan, Shandong, Shanxi, Shaanxi, Anhui, Jiangsu, Hubei, Jiangxi and Hunan till tomorrow the National Meteorological Centre (NMC), which renewed an orange alert for those areas said.
From Wednesday morning to Thursday morning, thick fog in parts of Beijing, Tianjin, Hebei, Henan, Shandong, Anhui, Jiangsu and Shanxi will reduce visibility to less than 200 meters, it said.
In extreme cases, visibility may fall below 50 metres in those regions, it added.
China has a four-tier colour-coded warning system for severe weather, with red being the most serious, followed by orange, yellow and blue.
Beijing Nanyuan Airport had cancelled 46 flights. In central China's Henan Province, low visibility led to traffic restrictions on 12 expressways.
The province also ordered all kindergartens and primary schools to close for the day.
The neighbouring province of Shandong upgraded its alert for heavy fog from orange to red Wednesday morning, and as of noon more than 155 flights from its capital Jinan had been delayed, cancelled or diverted.
Many regions have experienced heavy smog since last Friday, and it looks set to persist for the remainder of the week.
Data from Beijing Municipal Environmental Monitoring Center showed that the density of PM 2.5, particulate matter associated with hazardous smog, stood at 391 micrograms per cubic meter at noon in the city proper, indicating that the air is heavily polluted.
Many Chinese cities have suffered from frequent winter smog in recent years, triggering widespread public concern.
The central government has stepped up efforts to cut outdated production capacity and has dispatched inspection teams to provincial regions to supervise environmental measures at key industrial enterprises.