Pilot who crashed into Beijing's tallest building wrote about 'ending his life'

The crash damaged the facade of CITIC Tower, Beijing's tallest building. (AP: Han Guan Ng)

Chinese authorities say the pilot who crashed a small plane into Beijing's tallest building had written about "ending his life".

Their investigation found the man had insomnia and anxiety, and that the incident at CITIC Tower was caused by "personal reasons".

Social media discussion of the crash has been scrubbed as internet users raise questions about the incident.

The pilot who flew a small plane into Beijing's tallest building wrote in his diary about "ending his life", Chinese authorities say.

Their investigation concluded the cause of the June 26 crash was "personal reasons", according to a statement posted on social media by Beijing's Chaoyang district government.

The pilot, a 66-year-old Beijing man identified only by the surname Liu, died and 13 other people were injured.

The crash at CITIC Tower was caused by "personal reasons", according to Chinese authorities. (AP: Han Guan Ng)

None of the injuries are life-threatening and one of the injured has been discharged from the hospital, the government statement said.

The crash, which happened in a downtown skyscraper district as people were leaving work about 6pm, has raised questions about security in the Chinese capital.

It left a hole in the glass facade of the 108-storey CITIC Tower, nicknamed the "Zun" building because it mimics the shape of an ancient wine vessel of that name.

The pilot took off on a solo flight in the two-seat training plane from a general aviation airport in the outskirts of Beijing, the Chaoyang statement said.

Without identifying CITIC Tower, headquarters of one of China's largest state-owned conglomerates, the Chaoyang government said Mr Liu had deviated from his approved flight area and lost contact with the airport from which he took off before crashing into the building and dying at the scene.

Mr Liu had no fixed job, was divorced and lived alone, according to the statement.

He had insomnia and anxiety and his diary had multiple references to ending his life, it said.

Central Beijing, where China's leaders live and work, has strict airspace controls including a ban on drones and there has been speculation in the city's central business district, where the building is located, about what happened.

Discussion of the crash on Chinese social media has since been scrubbed.

Police and security set up cordons around the building after the crash. (Reuters: Maxim Shemetov)

Internet users were still seeking answers in posts beneath the online statement before they were swi