BEIJING - Severe smog continued to shroud northern China and even worsened late Monday, disrupting life in dozens of cities.

The education bureau in Zhengzhou, capital of central China's Henan province, ordered all primary schools to cancel classes for the next two days.

Northeast China's Liaoning province saw its most severe smog in seven years, with extremely poor visibility closing 18 expressways in the province.

Tianjin airport said it suspended service from 8:30 pm Sunday to 10 am Monday, leaving 131 flights canceled and 75 delayed.

Meanwhile, all expressways in the northern municipality of Tianjin were closed.

Local authorities in Tianjin increased public transportation capacity by 15 percent to accommodate passengers, as cars have been ordered to run on alternate days for five days until midnight Wednesday.

Beijing also increased its public transport and implemented the same odd-even number plate rule.

The Beijing municipal environmental protection bureau has introduced a spate of pollution reduction measures, including vehicle restrictions, to help cut PM2.5 pollutant emissions by over 20 percent.

In the eastern province of Shandong, over 100 toll gates on four expressways were closed and some flights in the provincial capital airport were delayed by more than two hours.

Smog started to envelop Beijing, Tianjin and the provinces of Hebei, Henan and Shandong over the weekend. It is forecast to clear Thursday. Over 20 cities have issued red alerts for smog.

On Monday, the PM2.5 reading in many cities in northern China, mainly in Hebei and Henan, exceeded 500 micrograms per cubic meter.

The reading at one monitoring station in Shijiazhuang, capital of Hebei, exceeded 1,000 micrograms per cubic meter at 1 pm Monday.