Authorities in Kunming are investigating multiple intrusions by drones into the restricted airspace of the city's airport.

Drones have been flown into the 1,028-square-kilometre restricted area of Changshui International Airport, posing risks to flight safety, news portal www.yunnan.cn reported. Local officials appealed to the public to report any sighting of drones in the area.

Mainland China exerts tight control over its airspace and maintains very strict regulations governing civilian drones. They must have flight permission from aviation authorities and are banned from entering a 15-kilometre range near airports and from flying higher than 100 metres on flight paths elsewhere. Anyone found in violation of the rules is liable to detention of five to 15 days.

Advances in unmanned aircraft technology around the world have made drones highly popular in China in recent years, with videographers, technology fans and even aspiring businesses investing in the aircraft for recreational and professional purposes. Many universities are starting or expanding their curriculum involving drones.

In 2013, four employees at a Beijing company were detained for carrying out surveys by flying a dronenear the capital's international airport without permission, forcing the diversion of two aircraft and causing multiple flight delays.

The suspects were detained on charges of "endangering public security" after their drone was detected by Civil Aviation Administration radars at an altitude of 700 metres and a speed of more than 100 km/h.

The aviation authority and police scrambled a helicopter to intercept the unmanned aircraft and eventually brought it to the ground.

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