China's civil aviation authority said it is investigating two smoking incidents on board a recent domestic flight that caused passengers to complain about their safety.

On Saturday night, a young man on board China United Airlines flight KN5216 from Chengdu, capital of Sichuan province, to Beijing, was found smoking in the plane's bathroom, according to a Monday morning statement by the airline on its Sina Weibo micro blog.

An onboard safety inspector confiscated the man's matches and cigarettes and asked him to refrain from smoking on board.

Passengers compensated for others smoking on flight

After a strong thunderstorm forced the flight to land in Taiyuan, Shanxi province, passengers and the plane's crewmembers caught a different passenger smoking near the cabin door. He was also asked to extinguish his cigarette, according to the statement.

The airline and the Civil Aviation Administration of China said they have jointly launched an investigation.

"Officials overseeing air transport safety have begun to look into the incidents and will make the result public once the probe is completed," said a publicity officer with the Civil Aviation Administration of China who refused to be named. She did not give any other details into the investigation.

After the plane landed, more than 20 passengers on board Flight KN5216 made complaints to airline officials at the Taiyuan airport that the flight's crewmembers had turned a blind eye to the smoking and that the captain was dismissive of passengers who asked for an explanation into the incidents.

A female passenger who identified herself as Deng told the Beijing Morning Post that she and other passengers "called the Taiyuan police after we landed to report the second smoker".

She also said that they asked the captain to have the airline re-screen the onboard luggage to rule out the possibility of other harmful materials on the plane. She said they feared that the smokers would also have lighters in their suitcases.

"But the captain just refused," she was quoted as saying.

When the plane finally resumed its flight and landed in Beijing early Sunday morning, 23 passengers did not leave the Beijing Nanyuan Airport until Sunday afternoon as they waited for an explanation and apology.

At the airport, Wu Gang, deputy general manager of China United Airlines, pledged to investigate the case and compensated each passenger 1,800 yuan ($290).

The airline has refused to reveal the name of the captain of the flight.

Smoking has been banned from onboard flights in China since 1988. The non-smoking rule began to apply to international flights that depart from China since July 1, 1993.

Despite the restrictions, there have been cases in which passengers have been caught smoking during flights.

In 2010, a woman from Shaanxi province was detained for seven days after she was caught smoking on a domestic flight. In 2012, a man was fined 200 yuan for onboard smoking before a Beijing-Saipan flight took off.

An officer from the police bureau at the Beijing Capital International Airport who spoke to China Daily on condition of anonymity, said airlines should inform the police if they find that flammable materials have been carried aboard a plane.

"However, as a matter of fact, it is very difficult for security workers at the airport to find a box of matches if a passenger deliberately hides one in his or her baggage because security staff mainly use metal detectors," he said.

"Smoking is completely prohibited on board the aircraft. … Such acts will incur heavy fines or administrative detention because it poses a severe threat to a plane's safety."

Zhang Qihuai, vice-president of aviation law research for the China Law Society, said a handful of smokers are unaware of the risks created by smoking on board a plane. Security workers at airports should strengthen their screenings of flammable materials, he added.