Studies dating to the 1940s found that low frequency sound energy could, depending upon intensity and exposure, cause dizziness, headaches, vomiting, bowel spasms, involuntary defecation, organ damage and heart attacks.

Sonic weapons are typically large and have to be mounted on vehicles. Until the Chinese development, which has no moving parts, they were powered by electricity to drive a magnetic coil to generate energy. This meant they needed a large and stable source of power.

The Chinese government launched the sonic weapon programme in 2017 and its conclusion is unlikely to be related to the months of anti-government protests in Hong Kong.

Professor Xie Xiujuan, lead scientist on the project, said the device was powered by a tube-shape vessel containing an inert gas. When heated, the gas particles vibrate and a deep, monotonous sound is emitted.

The prototype had passed field and third-party tests and the project team has completed its assessment of the device’s effects on the body, the academy said.

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On September 4, a panel of scientists and engineers representing the Ministry of Science and Technology met in Beijing and approved a design developed by Xie’s team for mass production.

“The panel suggested that the fruit of the project should be transformed into practical equipment as soon as possible,” the academy said.

In a photograph on the institute’s website, the device could be seen on a meeting room table as the experts deliberated. It looked similar to a rifle, with a stock, trigger and barrel.

Xie refused to reveal details of the device’s frequency or its effective range. She also declined to comment on its uses without approval from higher authorities.

So far, there have been no reports of Chinese soldiers or law enforcement officers using such equipment.