Arrivals and departures are both restricted area https://www.info.gov.hk/gia/general/...1202080367.htm

"Under sections 4 and 5 of the Aviation Security Regulation, any person who enters an airport restricted area shall have a valid permit unless he/she is an air-crew member, a passenger entering the area for the purpose of embarking on/disembarking an aircraft, or being escorted by a person authorised by the Airport Authority."