Heavy fog in northern, central and eastern China crippled traffic, closed highways and delayed flights Monday morning.

People cycle through dense fog in the port city of Tianjin in North China, Nov 28, 2011. The fog piled up since midnight on Monday and as of 8 am, all flights were delayed and most of the expressways toll stations are closed because of the heavy fog. [Xinhua]

China's National Meteorological Center (NMC) renewed its code blue alert to warn about fog in Jilin, Xinjiang, Gansu, Hebei, Shaanxi, Shandong, Zhejiang, Chongqing, Fujian and Yunnan provinces, the center said at 6 a.m.on Monday.

Visibility will drop to within one kilometer in some parts of the affected regions, and to as low as 200 meters in some areas, according to the NMC.

In northern China's Tianjin municipality, low visibility has led to the closure of 13 expressways, prompting warnings for dangerous road conditions and extended gridlock.

Thick fog has reduced visibility to less than 50 meters in the downtown areas of Tianjin, with visibility of less than 10 meters in the Hexi district in the early morning hours, according to the local police authorities.

Meanwhile, fog caused all flights to be delayed at the Tianjin Binhai International Airport on Monday morning, according to the airport operator.

Heavy fog also enveloped several cities in eastern China, with reports of major traffic jams in the cities of Wuxi in Jiangsu province and Jinan in Shandong province.

In northern Liaoning province, parts of the temporarily closed highways and disrupted flights resumed after the fog dissipated.