Beijing, Dec 7 (IANS): Heavy haze still shrouded China Saturday, with highways closed, and flights delayed or cancelled following an alert for haze.

Following a yellow alert for heavy fog Saturday morning, the National Meteorological Centre issued an orange alert for haze later, reports Xinhua.

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

The centre said on its website that from 2:00 p.m. Saturday to 2:00 p.m. Sunday, the Yangtze Delta region, central, and southern parts of north China, including central, and southern Beijing, will suffer pollution level four to five, with the heaviest level six in some areas.

Most of these areas will have moderate haze, while Jiangsu province, northern Zhejiang province, eastern Anhui province, and central and southern Hebei province will have heavy haze, said the centre.

More than 100 entries to highways in east China's Shandong province were temporarily closed due to haze, and some flights were cancelled or delayed at the Jinan and Qingdao airports.

The ministry of environmental protection said earlier this week that there were three major reasons behind the widespread haze: unfavourable weather conditions making it difficult for pollutants to diffuse, motor vehicle exhaust, and coal consumption for winter heating.