Smog returned to Beijing and much of northern China late Sunday after a short respite on Saturday, with the weather authorities warning residents to prepare for moderate to heavy pollution for much of this week, including New Year’s Day. Beijing and neighbouring Tianjin, Hebei, Henan and Shandong would be covered in pollution ranging from heavy to moderate because a cold front that arrived on Saturday was not strong enough to clear the pall, the weather authorities in the capital said. It did not say which areas would be worst affected. The warning came after parts of northern China, the Yangtze River Delta and Shaanxi province were blanketed by heavy pollution from December 19 to Friday. Beijing residents also woke to colder indoor temperatures in some areas on Saturday as the smog disrupted deliveries of natural gas, forcing the local authorities to impose temporary limits on heating. The Beijing Municipal Commission of City Administration and Environment said on its microblog that the heating limits went into effect on Saturday at government buildings, some public buildings, shopping malls, offices, and cultural and recreation venues. It said heating would be “back to normal as soon as possible” but did not specify when. READ MORE: Grey Christmas for Beijing with heavy smog prompting yellow alert The commission also called on residents and companies to minimise use of gas, electricity and heating. Beijing has issued two top alerts for smog so far this month, closing schools and limiting use of private cars to alternate days. The smog built up as winds blew in with PM2.5 pollutants – fine airborne particles that pose the greatest threat to public health. When wind from the south is blocked by the mountains north of Beijing, pollutants from the heavy burning of coal and other industrial work in some cities south of the capital accumulate and expand within the region, which shares an “air shed”. The meteorological authorities forecast that concentrations of PM2.5 in Beijing’s urban areas would be above 280 micrograms per cubic metre until Wednesday, rising to 350 micrograms per cubic metre in the southern part of the capital. READ MORE - Oops! Not so fast: Beijing wakes up to ... smog yet again, despite officials cancelling latest red alert The smog will also reduce visibility to less than 1km. The World Health Organisation recommends daily average exposures of no more than 25 micrograms per cubic metre. After a yellow alert on Christmas Day, Beijing residents were also warned to prepare for a grey New Year’s Day as smog would close in again around Friday. Yellow is the third-highest alert in the country’s four-tier system. Forecasters said only weak cold fronts were expected over the next 10 days. The authorities said residents should expect the smog to affect traffic and urged local governments to issue timely alerts.