People walk on the street amid a sandstorm in Lanzhou, northwest China's Gansu province, April 23, 2009. [CFP]

Parts of five provincial regions were affected, including Xinjiang Uygur Autonomous Region, Ningxia Hui Autonomous Region, Inner Mongolia Autonomous Region, and the provinces of Gansu and Shaanxi, the National Meteorological Center said.

The sandstorm hit the Gansu provincial capital of Lanzhou in the morning and reduced visibility to less than 500 meters, said Xu Dongbei, chief forecaster of the city's observatory.

Further west in Dunhuang, a tourist destination famous for Buddhist grottoes, the sandstorm lasted about 16 hours starting at 2:30 a.m. Maximum wind speeds reached 24.3 meters per second and visibility fell to 20 m.

"In terms of intensity and duration, [such a] sandstorm was rarely seen over the past decade," said Li Guanglin, chief forecaster of the city's observatory.

The sandstorm delayed two flights and forced many schools to suspend classes, local officials said.

"Agriculture might suffer serious damage from the sandstorm. I saw the strong wind swept away many greenhouse roofs, cotton seedlings and young grapes on the vine. Some trees and electrical poles were broken," said Gao Hua, of the Dunhuang Municipal Forestry Bureau.

The local government is calculating the losses.

In Yinchuan, capital of Ningxia Hui Autonomous Region, residents on the street were seen covering their mouths and noses tightly. Some wore a plastic box on their heads to keep out sand. At Hedong Airport, 12 flights were delayed.

Local meteorological experts advised citizens to stay indoors as much as possible, especially the elderly and children. They also warned people not to stand under billboards or trees.

Similar conditions prevailed in other provinces.

At Baita Airport in Hohhot, capital of Inner Mongolia Autonomous Region, 29 flights were delayed and three others were cancelled due to poor visibility and strong wind, stranding thousands of passengers, officials said.

Meteorological authorities in these provincial regions have forecast a temperature drop of up to 8 degrees Celsius and even frost after the sandstorm.

Sandstorm conditions would persist until Friday, the National Meteorological Center said late Thursday afternoon.

In addition to the five provincial regions, parts of Shanxi, Henan and Shandong provinces would also see dusty weather from Thursday night until dawn Friday, according to the forecast.

Although the provinces are adjacent to Beijing, the capital wouldn't be affected by the sandstorm, said Guo Hu, head of the Beijing Municipal Observatory.

He forecast strong wind would hit the city Friday, which has just seen showers Thursday.

Newlyweds brave a sandstorm to pose for their wedding photos in Lanzhou, capital of Gansu province, April 23, 2009. [Jiang Liansheng/China Daily