At least 1,000 drones have been put into use by police nationwide to assist in a wide range of operations, including tracking suspects, monitoring traffic and locating opium farms, according to the Ministry of Public Security.

The actual number is likely to be much higher, according to Li Mu, who works at the ministry's test center for special police equipment and oversees the quality of unmanned aircraft.

"The last time the ministry counted the number of police drones on the mainland was in September 2015," he said. "At that time, about 300 unmanned aircraft were used by nearly 150 police authorities in 25 provincial regions."

Li said since then many more drones had been added. "The Shenzhen Unmanned Aerial Vehicle Industry Association recently told us its members had sold about 700 drones to police authorities across China last year. Therefore, we can estimate a ballpark figure of at least 1,000 drones in service."

Shenzhen is the world's largest manufacturing hub for drones, as nearly 70 percent of consumer drones on the global market are made in the southeastern coastal city, which is home to more than 300 drone companies, according to the city's commerce bureau.

"To my understanding, a lot of local police continue introducing drones but have yet to report the condition of their fleets to the ministry, so the actual figure of police drones must be higher than our estimation," he explained.

Most of police drones are small- and medium-size quadcopters that use two pairs of identical fixed pitched propellers, Li said. Quadcopters are believed to be the most commonly used drones in civilian, business and public sectors because they are cheap and easy to control.

Li spoke to China Daily during the 2017 China Unmanned Systems Expo in Beijing, which closed on Friday. The three-day expo was jointly organized by the China Center for Aerospace Science and Technology International Communications and the China Association for Unmanned Vehicle Systems, displaying 140 unmanned aircraft from 103 domestic and foreign companies.

Reports show police in the cities of Beijing and Wuhan as well as Shandong, Jiangsu and Shaanxi provinces often deploy drones in operations.

Compared with manned helicopters used by police, drones have several advantages－they involve lower investment and maintenance cost, can be rapidly deployed, are suitable for use in dangerous circumstances such as chemical explosions or nuclear leaks and are not easily noticed, Li said.

Liu Daolin, deputy director of the Ministry of Public Security's police aviation management office, said local police departments are active and willing to use drones because they can perform a wide variety of tasks at low cost and low risk, he said. Liu previously estimated the number of police drones on the Chinese mainland would reach 1,000 by the end of 2020.