Beijing's air pollution reached dangerous levels for a second day Saturday, with the city's residents being advised to stay indoors to avoid the heavily polluted air.

The municipal environmental warning center issued a warning on its website after readings of PM2.5 -- airborne particles with a diameter of 2.5 microns or less that can deeply penetrate the lungs -- reached high levels around 5 p.m.

The heavy pollution is expected to last another three days, as weather conditions are preventing the pollutants from dispersing, the warning said, advising the public to stay indoors and to avoid strenuous exercise.

Real-time monitoring data on the center's website showed that all monitoring stations in the city's downtown area, as well as its eastern and southern suburbs, reported high pollutant readings at about 6 p.m.

Meanwhile, east and central China were enveloped in fog on Saturday, resulting in highway closures and flight delays in several provinces.

In Shandong province, 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 p.m. Saturday, affecting about 5,000 passengers, according to airport administration authorities in Qingdao.

In Jiangxi province, visibility in eight cities was reduced less than 500 meters. The fog forced five highways to close and delayed dozens of flights at an airport in the provincial capital of Nanchang on Saturday morning, according to local meteorological authorities. Endi