It started on the weekend as temperatures dropped and cities started burning coal to keep warm.
"Many cities in China, including the northeastern provinces, use coal as the major heat generator, which pushes up air pollution levels," said Zhang Bin, an official with Changchun city environmental protection department, according to state news agency Xinhua.
Farmers were also contributing to the haze by burning straw after the autumn harvest, according to Xinhua.
On Tuesday, heavy haze still hung over central Liaoning province, where authorities said visibility would be as low as 500 meters in some places. Heavy haze occurs when humidity is less than 80% and the visibility is less than two kilometers.
Mid-level haze was also recorded in parts of Beijing,Tianjin, and some areas of provinces Hebei, Henan, Shandong, Jilin and Heilongjiang. In areas of mid-level haze, humidity is less 80% and the visibility is between two and three kilometers.
Pollution levels 'off the charts'
Dozens of flights were grounded and highways closed after air pollution went off the charts in Shenyang in Liaoning Province, home to 8.1 million people, on Sunday.
Levels of PM2.5, the most harmful kind of particulates reached 1,400 in the city, 56 times the recommended levels set by the World Health Organization (WHO).
The WHO sets its maximum level at an average of 25 micrograms over a 24-hour period.
The dangerous acrid haze blanketed the provincial capital, slashing visibility. At least 87 flights were delayed or canceled as of 8 a.m. on Monday. Highways connecting Changchun and other cities in the province were completely or partially closed, state media said.
Local hospitals filled up with patients suffering from respiratory ailments and shops sold out of face masks.