Beijing: China maintained a yellow alert for smog on Saturday as high pollution levels in the north showed signs of abating. On Saturday morning, PM 2.5 density in most parts of Beijing ranged between 260 and 400 mg per cubic metre, far above the safety standard set by the World Health Organisation, according to a statement on the National Meteorological Centre (NMC) website. Regions, including Hebei, Shandong, Henan and Shaanxi provinces, will also be shrouded by heavy smog before a cold front gradually disperses the pollution, Xinhua news agency reported. Heavy rains will continue in the south. China has a four-tier warning system for severe weather, with red being the most serious, followed by orange, yellow and blue.