Story highlights Pollution levels soared in China's industrial zones

Airport officials say fog is thickest in years

(CNN) More than 20,000 people are stranded at an airport in Chengdu, China, as flights were grounded by heavy smog and fog, Chinese state-run media reported.

Multiple flights to and from the Chengdu Shuangliu International Airport in central China were canceled or delayed, while many were forced to land at other airports, China's Xinhua news agency reported, calling it "the worst fog to hit the ... city in years."

Heavy fog disrupts flights in and out of Chengdu airport, more than 10,000 passengers affected pic.twitter.com/Dqh7pyC8xb — CCTVNEWS (@cctvnews) December 4, 2016

Images from China Central Television (CCTV) showed weary passengers asleep in their airport seats and others eating instant pot noodles, while crates of luggage sat on the tarmac next to grounded planes.

The airport's runway was closed for nearly 10 hours, an airport statement said, saying the conditions had disrupted the most flights and the highest number of passengers in years.

Orange alert for air pollution issued for northern China as heavy #smog reduces visibility to less than 200 meters in some areas pic.twitter.com/G1oY6AONlL — CCTVNEWS (@cctvnews) December 4, 2016

Chengdu's air quality was measured at 280, a level within the "very unhealthy" category, according to the World Air Quality Index.

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