HARBIN -- Heavy smog shrouded northeast China on Monday, forcing the closure of schools, as well as disrupting flights and highways.
Meteorological authorities in Heilongjiang, Jilin and Liaoning provinces issued a red alert for thick smog or fog.
The fog will worsen in Harbin, Yichun, Daqing, Suihua, Jiamusi and Qitaihe cities in Heilongjiang with visibility of less than 100 meters in the next 24 hours.
The density of PM 2.5 -- airborne particles measuring less than 2.5 microns in diameter, exceeded 500 micrograms per cubic meter early Monday morning in Harbin, the provincial capital of Heilongjiang, with visibility of less than 50 meters in the city's downtown area.
All highways in Heilongjiang and Taiping International Airport in Harbin were closed due to the weather. Harbin's education authorities issued a notice to suspend classes at all primary and middle schools.
Some public buses also stopped running in Harbin. Many citizens had to walk or use other means of transport to work.
Highways were closed and flights disrupted in Jilin and Liaoning.
"The building 50 meters away cannot be seen clearly. I smelt irritative coal smoke when I opened the window of my house," said Sun Qi, a resident in Changchun, provincial capital of Jilin.
The meteorological station in Changchun issued a red alert at 2:45 a.m. Monday. Many pedestrians and traffic police were wearing masks.
With visibility of less than 100 meters, all 22 flights in Changchun Longjia Airport were delayed due to the foggy weather. Visibility was less than 500 meters in most of Jilin.
The weather also delayed trains and caused the closure of most of the highways in Jilin.
Sunday was the beginning of the heating season in Harbin. Heating supply companies have begun operation in Jilin.
A big difference in temperatures between day and night and the start of the winter heating season triggered the large-scale foggy weather, meteorologists said.
