Air pollution is known to cause heart and lung diseases, but new evidence shows that it may also cause cancer, according to the World Health Organization.

Experts suggested paying more attention to the possible harm smog might do to children.

"Children are more likely to be influenced by air pollution than adults because of their vulnerable physiology, but it's extremely rare to see such a young child diagnosed with lung cancer," said Kan Haidong, a professor from the School of Public Health at Fudan University, who has long been working on studies on the link between environmental factors and health.

Kan added that people should be cautious in making a direct connection between air pollution and a patient's cancer.

"It usually takes five to 10 years for a person to go from being exposed to a cancer-causing environment to being diagnosed with cancer," Kan said.

Kan also said that genetic factors may have contributed to the girl's condition.

According to the American Cancer Society, lung cancer is extremely rare among children and occurs mainly in older people. About two out of three people diagnosed with lung cancer are 65 or older, and the average age for diagnosis is about 70.

Kan said smoking is far likelier than environmental factors to cause lung cancer.

In China, smoking, including secondhand smoke, is the primary cause of lung cancer, accounting for more than 80 percent of cases, national health authorities say.

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