People found flying private paragliders without official permits may face criminal detention, Shanghai police said after 39 commercial flights at the city's two airports were disrupted on Thursday.

Three powered aircrafts, which were later identified by police as paragliders carrying nine people, flew without permits over Fengxian Bay in southern Shanghai's Fengxian district, the Shanghai-based Oriental Morning Post reported on Sunday.

Although the police and air force quickly began an emergency response, normal flight operations were seriously disrupted.

Under China's aviation regulations, all flights require permission before they leave the runway.

Pilots wanting to fly private aircraft in the Shanghai area must first seek a permit from the Civil Aviation Administration's East China office, said a senior air traffic controller at the Air Traffic Management Bureau on condition of anonymity.

"Such small aircraft usually fly at a low altitude that radars cannot detect. Therefore, we will not be able to give them directions and guide them out of the controlled airspace, which could result in casualties if a small aircraft encounters an airplane," he said.

"Airplanes usually fly at a about 9,000 to 10,000 meters. But it can be dangerous once a small aircraft reaches 600 meters, affecting the taking off and landing of airplanes," he added.

Operators or pilots of unlicensed flights face penalties even if there is no accident is caused, police told the Oriental Morning Post. Serious violations can mean fines, license suspensions and even criminal detention.

Chen Wenyu, a judge for the Aero Sports Federation of China's Hanggliding Associaton and the chief paragliding instructor at the Shanghai-based Flyingheart Club, told China Daily that power-based paragliders, unlike gliding parachutes, can rise to 7,000 meters at most.

But few people in China could reach that height because the engine of a powered parachute cannot function in such thin air and the pilot cannot endure the cold temperatures.

"We strongly denounce flights taken without approval. Our club's regular training was interrupted by some inspection due to this case. These irresponsible acts have greatly affected this emerging sport," he added.

People in East China usually go to Zhejiang province for gliding sports, said Chen, who has worked in the hanggliding field for more than 16 years.

A manager surnamed Li at the Yong'an Mountainous Villa Farm, which provides powered parachute services in west Zhejiang's Fuyang city, said they fly below 2,000 meters for safety reasons.

A day before the Shanghai paragliding incident, a powered parachute was reported to have intruded into the airspace of neighboring Jiangsu province's Nantong Xindong Airport. A China Eastern Air flight had to be diverted to Shanghai Hongqiao Airport as a result.