BEIJING, Dec. 5 -- Heavy smog and fog continued to hit many parts of east and north China on Thursday, causing traffic disruptions and school closures.

The National Meteorological Center on Thursday renewed a yellow alert for fog and smog as dense air continued to choke eastern and northern provinces, including Shandong, Hebei, Shanxi, Jiangsu, Zhejiang, Anhui and Jiangxi. The yellow alert is the third highest in China's four-level alert system.

With visibility reduced to less than 50 meters in places, many highways in east China's Jiangxi Province were closed on Thursday morning. A Xinhua reporter saw thousands of drivers stranded on the Changdong Highway in the provincial capital of Nanchang.

Classes were suspended on Thursday in all middle and primary schools as well as kindergartens in Nanjing, capital of east China's Jiangsu Province, after the municipal government on Wednesday evening initiated a red-coded emergency response to air pollution.

In the neighboring Zhejiang Province, lingering smog left the air quality in the cities of Shaoxing, Jiaxing and Jinhua at seriously polluted levels, according to the website of the provincial environment protection department.

The static weather and weak activity of the cold air have contributed to the smog, experts said.