A drone with a wingspan of 18 meters and a battery life of 30 hours is seen at the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Mao Siqian)

An agricultural drone is seen at the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Mao Siqian)

An exhibitor introduces a ground station product at the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Mao Siqian)

An unmanned helicopter is seen at the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Mao Siqian)

A palm-sized drone with an endurance of five minutes is seen at the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Mao Siqian)

A foreign businessman looks at drones at the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Mao Siqian)

A police drone is seen during the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Zhou Ke)

A fire-fighting drone which is still under development is seen at the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Li Sijia)

An exhibitor flies a drone used for mapping at the Shenzhen International UAV Expo 2018 in Shenzhen, south China's Guangdong Province, June 22, 2018. The expo kicked off here on Friday and displayed various types of unmanned aerial vehicles (UAV). (Xinhua/Zhou Ke)