China has been enveloped in smog again over the weekend.

At least 104 cities in 20 provinces in and near China's two largest industrial clusters were affected by the heavy smog, according to the Environmental Protection Ministry. Visibility in these areas were reduced to less than 10 metres.

An electronic screen and buildings are seen amid heavy smog at the financial district of Pudong in Shanghai December 6, 2013. China's stability-obsessed leadership has become increasingly concerned by the abysmal air quality in cities, as it plays into popular resentment over political privilege and rising inequality in the world's second-largest economy. REUTERS/Aly Song

East China's Shandong Province was forced to temporarily close more than 100 entries to expressways due to the haze on Saturday. Jinan and Qingdao airports were likewise forced to cancel and delay some flights.

In Hangzhou, Nanjing and Zhengzhou, about 250 flights were delayed or cancelled.

It was on Wednesday when haze started to hit China's central and eastern areas. He Lifu, CMC's chief meteorologist, said this latest haze wave was the severest so far this winter.

The air quality indexes in nearly 80 cities on Sunday, including Beijing and parts of Zhejiang, Jiangsu , Anhui , Shandong , Henan and Hebei provinces were more than 200, meaning the air was "heavily" or "severely" polluted.

Unfavourable weather conditions, motor vehicle exhaust and coal consumption for winter heating were the identified reasons by the Ministry of Environmental Protection for the widespread haze.

Video Source: Youtube/ CCTV News

"Locally generated emissions remain the prime cause of the severe smog, but it is exacerbated by the static atmospheric condition that traps the pollutants," Professor Chai Fahe, vice-president of the Chinese Research Academy of Environmental Sciences, was quoted by South China Morning Post.

At least four car accidents, with six people dead, have resulted from the latest wave of smog.

Some residents, the China Central Television reported, are now busy booking flight arrangements to escape the smog.

"I want to go to Sanya. Sanya's air quality is better than here, and the scenery is also good."