BEIJING, March 28 (Xinhua) -- Since Monday, China's northern regions have seen their fourth round of sandstorms this year, the China Meteorological Administration (CMA) said Wednesday.

So far, the sand and dust have affected Beijing and Tianjin Municipality, Shanxi, Hebei, Liaoning, Jilin and Heilongjiang provinces, as well as Inner Mongolia and southern Xinjiang, according to the National Meteorological Center of the CMA.

The center said that an area of 1.5 million square kilometers, or around one-sixth of the country, has been affected by the weather.

Statistics released by the Ministry of Ecology and Environment showed that sand and dust swept northern parts of the Beijing-Tianjin-Hebei region on Wednesday morning. The air quality index (AQI) in some cities of the region reached 500.

The sand and dust will last until Thursday in the region.

Visibility was low in Beijing on Wednesday. The city issued a blue alert for dust, the lowest in China's four-tier weather alert system, this morning.

The meteorological center said the level of PM10 in Beijing soared from 282 micrograms per cubic meter to nearly 2,000 from 5 a.m. to 7 a.m. on Wednesday.

Neighboring Tianjin Municipality issued an orange alert for heavy air pollution on Monday. Measures such as traffic controls on heavy trucks in the city, pollutant emission cuts in factories and suspension of work at construction sites have been taken in Tianjin.

Cities in northeast China's Liaoning Province also saw floating dust and sand at noon on Wednesday.

The provincial meteorological center issued a blue alert for gales on Wednesday morning. Some coastal areas and flights will be affected by strong wind.