People visit the 4th Shenzhen International UAV Expo in south China's Guangdong Province, June 20, 2019. The Drone World Congress 2019 and the 4th Shenzhen International UAV Expo opened here on Thursday. Over 400 enterprises will show more than 1,000 drones at the event. (Xinhua/Wang Feng)

Photo taken on June 20, 2019 shows the venue of the 4th Shenzhen International UAV Expo in south China's Guangdong Province. The Drone World Congress 2019 and the 4th Shenzhen International UAV Expo opened here on Thursday. Over 400 enterprises will show more than 1,000 drones at the event. (Xinhua/Wang Feng)

People visit the 4th Shenzhen International UAV Expo in south China's Guangdong Province, June 20, 2019. The Drone World Congress 2019 and the 4th Shenzhen International UAV Expo opened here on Thursday. Over 400 enterprises will show more than 1,000 drones at the event. (Xinhua/Wang Feng)