XI'AN -- Xi'an, capital of northwest China's Shaanxi province, has issued a red alert for severe air pollution, with elementary and high schools and kindergartens suspended Wednesday.

The red alert, the most serious in the four-tier alert system for air pollution, came into effect Wednesday, as did the introduction of odd-even plate restrictions on vehicles, cutting traffic on roads by about half.

Outdoor activities have also been suspended, according to the city's heavy air pollution emergency response office.

Companies and public institutions are encouraged to ask their employees to work from home under the red alert.

The provincial weather bureau said heavy air pollution would last for days in Xi'an and the neighboring city of Xianyang and would not disperse until after Saturday in some parts of Xi'an.