A plane passenger has threatened a flight attendant with a fountain pen, forcing an Air China flight bound for Beijing to make an unscheduled landing, according to the country's civil aviation authority.

In a brief statement on its website, the Civil Aviation Administration of China said a male passenger, who it did not identify, on Air China Flight 1350 attempted to use the pen to hold the flight attendant "under duress".

Passengers and crew were unharmed, the statement said, without providing any further details.

Chinese police said preliminary investigations found the 41-year-old passenger, identified only by his last name Xu, had a "history of mental illness".

The flight took off from Changsha, the capital of southern Hunan province, at 8:40am (local time) and was scheduled to arrive at Beijing Capital International Airport at about 11:00am, according to local media reports and flight tracking websites.

But it made the unscheduled landing at Zhengzhou Xinzheng International Airport, in central Henan province, at 9:58am, according to an earlier post on Air China's official Weibo microblog.

Air China said in the post that the plane made the unscheduled stop due to "public safety reasons", and that police and civil aviation authorities were handling the situation.

The Beijing News said on its Weibo page that a passenger described being awoken by a scream coming from the front of the plane and that "nobody knew what was going on".

The Xiaoxiang Morning Herald quoted a passenger as saying that the disturbance occurred in the first or business class cabins but that the curtains separating those sections from economy class were pulled tightly shut.

The passenger looked out the window and saw many police cars, ambulances and fire engines parked outside the plane as it was landing in Zhengzhou, the newspaper said in a Weibo post.

The passenger described seeing armed personnel in camouflage uniforms assembled in two or three rows.

AP/Reuters