BEIJING, March 28 (Xinhua) -- The national weather observatory continued its blue alert for sandstorms on Wednesday, forecasting wind and dust for north China.

From Wednesday evening to Thursday, parts of Inner Mongolia, Ningxia, Gansu, Shaanxi and Xinjiang will be affected by the dust, said the National Meteorological Center (NMC).

Parts of Inner Mongolia, Ningxia and Gansu will be swept by sandstorms.

Since Monday, the country's northern areas have witnessed their fourth wave of dusty weather this year, affecting more than 9 provincial-level regions and covering an area of 1.5 million square kilometers, NMC data showed.

The sandstorms led to serious air pollution Wednesday. Monitoring stations in Beijing showed PM10 and PM2.5 readings jumped to nearly 2,000 micrograms per cubic meter and over 300 micrograms per cubic meter, respectively.

The center suggested people in the affected regions close their doors and windows at home and wear masks outdoors

China has a four-tier color-coded system for severe weather, with red being the most serious, followed by orange, yellow and blue.