An electronic screen and buildings are seen amid heavy smog at the financial district of Pudong in Shanghai.

More than half of China's military airfields have flight paths that are obstructed by tall buildings, causing accidents and airport closures, Chinese state media reported on Friday.Nearly 100 accidents have occurred at military air bases due to high-rise buildings and development in the past 20 years, the website of the ruling Communist Party's mouthpiece, the People's Daily said.The problem has become so great that more than 10 military airfields have been forced to close or move."With the continuous expansion of the scale of cities, a relatively large number of military air bases have merged with new city districts and development zones, leading to a deterioration in clean airspace," the website said.Requirements for "clean" airspace around military airports are more strict due to special training demands, it said, citing the People's Liberation Army General Staff Headquarters.There are more than 1,000 buildings that violate height restrictions near military air bases acrossChina and some structures are built on landing and take-off flight paths, leading to serious safety problems, the news agency said.China's military frequently expresses concerns about urban development infringing upon its bases. China approved a law to strengthen protection of military bases in June.But China also recently relaxed restrictions on low-altitude flying in its mainly military-controlled airspace in a boost to the growing helicopter industry.

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Air safety has been in focus internationally after a series of deadly crashes around the world in recent weeks.