Flights were delayed and thousands of passengers were stranded at airports in China on Dec. 21, as heavy fog continued to shroud large areas of the country.

Shuangliu airport in Chengdu, capital of southwest China's Sichuan Province, was closed for four hours in the morning as mist reduced visibility to only 20 meters, according to Lu Junming, an airport official.

A total of 121 flights entering or leaving the airport were delayed, 11 were cancelled and eight others were forced to land in the nearby cities of Kunming, Chongqing and Guiyang.

More than 11,000 passengers were stranded at the airport until the fog gradually cleared around noon.

The fog was caused by high humidity and low temperatures, according to the local meteorological observatory.

At Jinan international airport in east China's Shandong Province, which has been cloaked in mist since Dec. 19, visibility in the morning was less than 50 meters on Dec. 21. Some 110 flights were affected.

More than 310 flights at the airport were postponed or cancelled during the period of 6 p.m., Dec. 19, to 3 p.m., Dec. 21.