Mannequins in riot gear, armoured cars and drones line a police equipment and "anti-terrorism technology" trade fair in Beijing as vendors seek to profit from China's huge internal security budget.

The country is estimated to have more than 180,000 protests each year and the ruling Communist Party spends vast sums on ensuring order -- more even than on its military, the largest in the world.

Shields, batons, gun-sights on wooden rifles and more were on display at the event last week, where the capital's own police force promoted a lie-detection system.

Two men in black uniforms marked "SWAT" inspected a pair of night-vision goggles, while a group of policemen who said they were from Jiangxi province in the south looked on as a bomb-disposal robot was put through its paces.

"The country is giving huge support to police spending," said Lu Hui, a salesman for "Robostep", a two-wheeled self-balancing scooter akin to a Segway, which he said was used by police patrolling Beijing's Tiananmen square.

Another stall sold wireless microphones it claimed are used to pick up disturbances in the square, under tight security since 1989, when it was the scene of huge pro-democracy demonstrations later crushed by authorities, killing hundreds.

"Our government makes an annual budget for public security, and we have a much bigger budget than before," said salesman Ryan Fan, standing in front of a display of black security vests, bulletproof helmets and clear plastic shields.

"These products are mainly for anti-riot policemen," he added.

China's domestic security budget across all levels of government is 769 billion yuan ($125 billion) this year, more than the country officially plans to spend on its armed forces, and an increase of more than 200 billion yuan since 2010.

Billions of the internal security budget, which also covers mundane items such as food safety and running courts, is earmarked for "stability maintenance", a term used to justify arresting protesters and surveillance of dissidents.

"We have a lot more to spend, particularly on anti-terrorism," said one of the Jiangxi police delegation, declining to be named because of the nature of his work.

Dozens of vendors offered the latest in surveillance technology, from scanners which pick up mobile phone signals to secret bugging devices and drone aircraft.

One remote-controlled helicopter had a starting price of 100,000 yuan. "Police departments across China are already using it," said a salesman for the Beijing-based company Seven Dimension Information.

It is not only domestic firms who supply the market.

Inspirational music flowed from a display of Mercedes police vehicles, while Ford and Hyundai cars emblazoned with the word "Police" sat on raised white podiums.

One stall displayed an apparently Australian-made drone with a built-in video camera, and pictures of residential districts taken by the lightweight craft lined the walls.

Western companies have in the past been the focus of criticism for helping Chinese authorities set up vast surveillance systems.

"I think surveillance technology is something that is growing in our concerns," said Kaye Stearman, of Britain-based advocacy group Campaign Against the Arms Trade.

A ban on EU arms exports to China -- introduced as a reaction to the Tiananmen crackdown -- does not outlaw exports of many technologies which could be used for internal repression, she added.

Analysts say that the rise in security spending has matched a growth in protests around China. The country had an estimated 180,000 demonstrations -- or "mass incidents" -- in 2010 and numbers have risen since, according to academics.

Chinese authorities have to increase police manpower to "take care of fast-growing mass protests on the streets and 'potential' threats on the Internet", said Chih-Jou Jay Chen, a researcher at Taiwan's Academia Sinica.

Government departments responsible for maintaining stability have "asked, seized, and fought for power and resources" in recent years, he told AFP.

China's new head of public security Meng Jianzhu was not given a seat on the ruling Communist Party's Politburo Standing Committee, its highest-ranking body, during the country's recent leadership transition, prompting speculation that the security apparatus may be reined in.

But vendors at the fair did not expect any spending cuts.

"The money will continue to increase, the stability maintenance model will continue," said Chen Dahai, a former detective who left the force to sell fingerprint-detecting devices.

"The police have a lot more money, they can barely spend it all."