Beijing and at least seven other provinces and municipalities were blanketed by heavy smog yesterday, with expressways closed and flights cancelled. Mainland media reported that expressways in Beijing, Tianjin , Hebei , Liaoning , Heilongjiang , Shandong , Jiangsu and Hubei were blocked to prevent traffic accidents due to poor visibility. Those closed included 10 expressways in Hebei province linking Beijing, Tianjin and northeastern China. In Beijing, at least 35 domestic and international flights were cancelled and 37 flights delayed due to the heavy smog. Beijing's observatory said visibility was reduced to between 500 and 1,000 metres. The capital's environmental watchdog blamed the smog on heavy air pollution, saying readings for fine-particle air pollutants from 35 monitoring stations in Beijing were impermissibly high. Members of the public were told to stay indoors if possible. At least 40 highway sections in Shandong were shut down yesterday. All highways in Harbin , the capital of Heilongjiang province, were closed. One person was killed last week and 20 others injured when 30 vehicles collided in three separate accidents because of smog and poor visibility on the Tangshan-Tianjin expressway that links Tianjin, Hebei and northeastern China.