Police are investigating claims that a drone flew over the chief executive's office in Hong Kong on Monday evening. According to a police source, an officer heard some noises at about 5.30pm. The officer and a woman security officer then saw the black unmanned aircraft, which was about 20cm to 25cm wide, flying at a height of about five metres above the ground. It stayed in the air for about seven minutes then fell among some plants at the site, the source said. Officers did not find anyone suspicious in the area. After a preliminary investigation, the force classified the case as a request for police investigation. No one has been arrested. Three arrested for flying drones over Hong Kong Formula E event According to the Civil Aviation Department, remote-controlled flying devices should not be flown within 5km of any aerodrome or within 50 metres of any person, vessel, vehicle or structure not under the control of the operator. The take-off and landing area should be properly segregated from public access. Civil aviation law requires only those operating drones weighing more than 7kg for leisure or commercial photography to submit an application to the department. During the Formula E races in October 2016, three men were arrested for flying a drone over the racetrack area. Each of them was fined HK$2,000 (US$255) by the court last year.