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

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

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.