China has a found a novel way to tackle its massive air pollution problem: Putting up a giant air purifier the size of an industrial smokestack in the middle of a smog-plagued city.

Instead of pumping out billows of black smoke like the chimneys rising from factories in the northern province of Shaanxi, the 60-meter (197-foot) tall structure on the outskirts of the regional capital Xian blasts clean air.

Standing between high-rises, the device is capable of cleaning between five million and 18 million cubic meters of air each day, depending on the weather, season, and level of pollution, according to a report by the Chinese website Thecover.cn.

The tower can reduce the density of PM 2.5 -- the tiny airborne particles considered most harmful to health -- by between 10 and 19 percent in a 10 square kilometer (3.9 square mile) area, the website said.

PM 2.5 can play a role in heart disease, stroke, and lung ailments such as emphysema and cancer.

Pollution is so bad in many regions of China that people often wear masks on the street and buy expensive air purifiers for their homes Fred DUFOUR, AFP

For now, the facility -- which was built in June 2016 -- is just an experiment.

But its designers hope to build similar towers across the city.

Cao Junji, an environmental protection expert at the Chinese Academy of Sciences, told reporters that it would take about 100 towers to cover the city of 1,000 square kilometres (385 square miles).

A lot of people have questioned the device's effectiveness, he said.

"I questioned it myself. But when we finished, the results were quite good. They met our expectations."

China's government declared "war" on pollution in 2014.

Pollution is so bad in many regions that people often wear masks on the street and buy expensive air purifiers for their homes.

This past winter, China cut production for many steel smelters, mills and factories.

China's air quality improved in 2017, with the average level of PM 2.5 particles falling by 6.5 percent in 338 cities, according to environmental authorities Fred DUFOUR, AFP

The environment ministry imposed tough anti-pollution targets on 28 cities around Beijing, with at least three million homes expected to switch from coal to gas or electric heating.

China's air quality improved in 2017, with the average level of PM 2.5 particles falling by 6.5 percent in 338 cities, according to environmental authorities.

A University of Chicago study found last year that air pollution in northern China had cut life expectancy by three years compared with the south of the country.

But a new study by the university in March found that China had made so much progress against smog that life expectancy could rise by more than two years.