Beijing, Jan 3 (IANS): Twenty-five Chinese cities are on red alert due to severe air pollution, officials said on Tuesday.

This is the first red alert issued in the new year in China, following similar warnings in late 2016 in the northeastern region of the country, including capital Beijing, Efe news reported.

Beijing, along with 20 other cities, have been under an orange alert for days while 16 others, including Xian, have been under the yellow alert.

In total, 72 Chinese cities are under some sort of pollution alert at present.

Meanwhile, the Beijing-Tianjin-Hebei region has extended its alert until Saturday night, the Ministry of Environmental Protection announced on Tuesday.

In some parts of the region pollution is expected to reach very serious levels with concentrations of PM 2.5 (the most dangerous) particles of up to 300 micrograms per cubic meter, while the World Health Organization recommends a maximum level of 25.

However, according to forecast for the northeast region, a cold front on Sunday is likely to disperse the thick layer of smog.

The declaration of pollution alerts are accompanied by different levels of restrictions on traffic, schools, activities of polluting industries and the construction sector.

But a ministry report released Monday acknowledged many companies were ignoring these measures and continuing with their activities as usual leading it to probe the worst affected areas for non-compliance.

The smog has reduced visibility to less than 50 metres, leading to various problems at airports and highways in large cities such as Chengdu and Tianjin, the National Meteorological Centre said on Tuesday.