A farmer checks the hothouse damaged by the gale in Sanlei Township of Wuwei County in Wuwei City, northwest China's Gansu Province, April 25, 2010. The Hexi Corridor had been hit by the most serious sandstorm in 9 years since Friday. [Xinhua]

The latest round of sandstorms started on Saturday afternoon, sweeping Xinjiang, Qinghai, Gansu and Inner Mongolia.

In Gansu, the sandstorm leveled 547 houses and damaged 812 others.

At 7:10 pm on Saturday, people in Minqin county could barely see anything in the strong wind, a situation local meteorologists called the "black wind."

"A strong wind with heavy sand hit me like a wall and the sky suddenly became dark," a Minqin resident said.

Strong sandstorms hit most of Inner Mongolia on Saturday afternoon, with wind speeds of up to 22 meters a second, said Sun Yuegang, a forecaster with the local meteorological bureau of Alashan League. Visibility was only 50 meters at the peak of the sandstorms.

Latest satellite maps show that the strong sandstorms over the weekend affected 6.7 million people and 135 million hectares of land in Xinjiang, Qinghai, Gansu and Inner Mongolia, China National Radio reported on Sunday.

A cold front from Xinjiang to Gansu and high temperatures in desert areas caused the sandstorms, experts said.

"Every year from March to May, the frequent cold air and high temperatures in deserts are likely to form sandstorms," said Qiao Lin, chief forecaster with the China Meteorological Administration.