The heavy metal part tore through the factory's canvas roof in Shanghai's Songjiang district on Monday night, according to the Shanghai Morning Post. No one was injured.

China's aviation authority confirmed the metal plate was part of a Boeing 777 passenger aircraft, most likely part of a landing gear compartment door.

A factory worker told local media: "It is incredible that no one was killed, but even more scary that a plane is flying around with part of its landing gear broken."

The curious case was only made public after a woman posted photos of the errant plane part on the Chinese social media platform Weibo, the Shanghaiist reported.

A sticker on the triangular-shaped metal part that reads "made in Canada", as well as an order and unit number.

The photos also show appendages attached to the metal plate that appear to have snapped off.

China's Civil Aviation Administration (CAA) was checking flight details of aircraft known to have been flying over Shanghai on Monday night to try and identify the plane that had lost the cover plate.

An aviation official told the Chinese state-run news agency Xinhua that the airline involved would be given an official warning and would be liable for any damage to the factory as a result.

"Although no one was injured by the falling plane part, it could have posed a threat to the air route," said a spokesman for the CAA.

An unnamed aviation expert told the Shanghai Morning Post that a missing cover plate would not affect the working of the undercarriage or the plane's ability to land.

He said it might have fallen due to loose parts, ageing or some kind of impact to the aircraft and may have dropped from as high as 1,800 metres above the ground.

The metal part was moved to the Songjiang district police station to be analysed, the Shanghaiist reported.