Poor visibility brought on by heavy smog in Beijing on Friday caused temporary closure of several highways in the city.

The heavy smog led to over 200 flight delays by Friday noon, according to the micro blog of the Beijing Capital International Airport. The Beijing municipality's heavy pollution emergency response headquarters issued a blue alert for heavy pollution on Thursday afternoon, saying smog will hit central Beijing and its southern suburbs on Thursday night. It then upgraded its alert to yellow on Friday as the smog worsened in the city. China has a four-tier warning system for smog, with red as the most severe, followed by orange, yellow and blue. Beijing Education Committee issued an urgent notice calling for kindergartens, primary schools and middle schools to ban outdoor activities on Friday. A cold front is expected to arrive on Saturday to disperse the smog.

cuijia@chinadaily.com.cn