Tourists wearing facemasks walk by the Temple of Heaven in Beijing, as Saturday's PM 2.5 air quality index reached around 470-490.(Photo/Xinhua)

Citizens walk on a bridge in the fog in Hefei, capital of east China's Anhui Province, Jan. 13, 2013. Dense fog on Sunday hit China's east and central regions from the northeast to the south.(Photo/Xinhua)

Citizens ride in the fog on a street in Ganyu County of Lianyungang City, east China's Jiangsu Province, Jan. 13, 2013. Dense fog on Sunday hit China's east and central regions from the northeast to the south.(Photo/Xinhua)

A man takes photos on the fog-shrouded Kaifeng Road in Guilin, southwest China's Guangxi Zhuang Autonomous Region, Jan. 13, 2013. Dense fog on Sunday hit China's east and central regions from the northeast to the south, causing serious air pollution.(Photo/Xinhua)

A woman rides on the fog-shrouded Chongxin Road in Guilin, southwest China's Guangxi Zhuang Autonomous Region, Jan. 13, 2013. Dense fog on Sunday hit China's east and central regions from the northeast to the south, causing serious air pollution.(Photo/Xinhua)

Vehicles move in the fog on a street in Changchun, capital of northeast China's Jilin Province, Jan. 13, 2013. Heavy fog hit Changchun on Sunday.(Photo/Xinhua)

Buildings are blanketed in dense fog in Changsha City, capital of central China's Hunan Province, Jan. 12, 2013. A fog hit Changsha on Saturday.(Photo/Xinhua)

Heavy fog enveloped a large swathe of East and Central China on Saturday, causing highway closures and flight delays in several provinces.

Beijing was shrouded in dense smog for a second straight day on Saturday. The smoggy weather will not clear up until Monday, the city's environment monitoring center said.

Reporting that Beijing's air is heavily polluted, the center said readings for PM 2.5, or airborne particles with a diameter of 2.5 microns or less - small enough to deeply penetrate the lungs - reached the range of 470-490 on Saturday morning.

The elderly, children and those suffering from respiratory and cardiovascular diseases in the capital have been advised to stay indoors to reduce exposure to polluted air.

Meanwhile, heavy fog has blanketed other regions including Hebei, Tianjin, Shandong, Henan, Jiangsu, Anhui, Jiangxi and Hubei. In Shandong, more than 20 highways were closed, as the fog reduced visibility in some areas to less than 50 meters, the provincial meteorological center said.

A total of 63 flights in and out of Shandong's eastern coastal city of Qingdao had been canceled or delayed by 2 pm on Saturday, affecting about 5,000 passengers, according to airport authorities in Qingdao.

In Jiangxi, visibility in eight cities was reduced to less than 500 meters. Five highways were closed and dozens of flights delayed at an airport in the provincial capital of Nanchang on Saturday morning, according to local meteorological authorities.