Transport ground to a halt as heavy fog enveloped southwest China's Sichuan Province Wednesday forcing airports and expressways to close to traffic.

According to local meteorologists, the cities affected included Chengdu, the provincial capital, Dazhou, Leshan and Meishan.

In Chengdu, Shuangliu International Airport closed at around 6:50 a.m., as visibility fell below 50 meters. It resumed normal operations at around 11 a.m. when the fog dispersed.

During the closure, 105 flights to and from Shuangliu were delayed and more than 10,000 passengers were stranded. Some of the incoming flights were forced to land at airports in nearby Chongqing and Kunming cities.

At least four expressways, including the routes between Chengdu and Dujiangyan and between Dazhou and Chongqing, were closed in the morning.

Meterologists said the fog was caused by coincidence of high humidity on the ground and a clearing sky, typical of weather often seen in early winter in Sichuan.

Beijing, the nation's capital, was also blanketed in fog early Wednesday.

Prior to 9 a.m., visibility at the Capital International Airport in Beijing was around 50 meters, rising to 500 meters after 10 a.m.. Many flights were delayed, said a north China aviation control department spokesman, but without revealing the exact number.

Tianjin sections of Beijing-Tianjin-Tanggu and Beijing-Shanghai expressways were closed in the morning because of the fog.

Meteorologists in Beijing believed the fog spread to Beijing from the adjacent Hebei Province.

According to the National Meteorological Center, weak cold air will affect north China Thursday dispersing heavy fog in northern regions, including Beijing.