The most severe and lasting smog since the winter began is not expected to clear until Monday, with eastern and central regions of China facing severe pollution.

The smog struck even as the Ministry of Environmental Protection (MEP) said Tuesday that the emission reduction goal of four major air pollutants will be reached by the end of 2013.

The pollution affecting the regions is the most severe mid- to heavy-scale smoggy weather so far this winter, said He Lifu, chief forecaster at the National Meteorological Center (NMC), in a report on the NMC's website.

The heavy smog started accumulating over the weekend, and the NMC issued the third consecutive yellow alert for smog and fog on Wednesday. The yellow warning is the third most serious alert in China's four-tiered system, with red being most severe, followed by orange, yellow and blue.

In Shanghai, the Air Quality Index (AQI) hit 317 at noon on Monday, crossing the threshold of 300 into "severe" pollution, according to the Shanghai Environmental Monitoring Center. This led to the suspension of outdoor activities at school.

In neighboring Jiangsu Province, all of its 13 cities suffered heavy pollution on Monday. Nanjing, capital of Jiangsu, has issued a red alert, which means kindergartens through high schools will be closed Thursday.

"It's quite shocking that Nanjing should have smog this heavy," said Li Zhi, a soil environmentalist who lives in the city. "You look at buildings only 50 meters away and they're hidden in fog. I keep the windows in my apartment closed all the time."

Wang Gengchen, a research fellow with the Institute of Atmospheric Physics at the Chinese Academy of Sciences, told the Global Times the formation of strong smog is due to two reasons, accumulation of pollutants and weather conditions.

"There is a lack of cold air flow, which is disadvantageous to the dispersal of accumulated pollutants," he said.

However, Zhuang Guoshun, director of the Center for Atmospheric Chemistry Study at Fudan University in Shanghai, believes the recent breakout of large-scale smoggy weather is only a continuation of the existing pollution situation.

Since January this year, most parts of China have been stricken by heavy smog, especially in northern China.

Now it's winter, when the meteorological conditions become worse, the pollution immediately returns, Zhuang said.

"In terms of PM 2.5 (particulate matter under 2.5 micrograms), Shanghai doesn't differ a great deal from Beijing. If Beijing reaches a PM 2.5 density of 70 micrograms per cubic meter, then Shanghai is close behind at 50 micrograms," Zhuang said. "What happens in Beijing and Tianjin will surely happen to the Yangtze River Delta area."

On Tuesday, the MEP revealed at a meeting that the country will reach its goal of reducing emissions of the four major air pollutants contributing to PM 2.5 (chemical oxygen demand, ammonia, sulfur dioxide and nitrogen oxides) by 2 percent by the end of 2013.

However, Zhuang remains skeptical of the goal, noting there's a huge increase in motor vehicles, which contributes to the emission of nitrogen oxides.

Smoggy weather is predicted for Thursday in Jiangsu, Anhui, Zhejiang and Shandong provinces, as well as in Shanghai.

"The smoggy weather might entirely clear up by December 9. A strong cold air flow will come to the central and eastern regions," He, the NMC forecaster, said. "From the afternoon of December 8, the pollution will start clearing up from the north to the Yangtze River Delta."