In yet another instance of appalling behaviour on a flight, a Chinese man boarded the plane, walked to the emergency exit and opened it.
He then sat down by the open door and gazed outside.
When asked to explain his action, he replied nonchalantly: "The door is not important."
The incident happened at Nanjing Lukou International Airport on a China Southern Airlines flight, The Beijing News reported.
The flight was due to travel from Nanjing, in Jiangsu province, to Nanning, in Guangxi province on Monday.
Nobody tried to stop the man from opening the door, Hong Kong newspaper South China Morning Post quoted witnesses as saying.
The man, who has not been identified, was able to open the door with little effort, they said.
The nearest flight attendant was helping other passengers put their luggage in overhead compartments at the time.
Police detained the man and said they would keep him in jail for 10 days, which means he will be spending next week's Chinese New Year holiday in prison, the report said.