Drug-rehabilitation workers criticised the sentence, saying the judge placed too much moral onus on teenager Lee Wai-man.
Caritas drug treatment service social worker, Eddie Leung Yin-mai, said: 'The boy has been made a scapegoat just because the judge wants to send a message to the public that this is a serious crime.
'The penalty should be handed down based on justice [alone] rather than the moral impact on society. For a 19-year-old, five years is way too heavy and it is not going to help reform the youngster.'
Chan Shu-cheuk, principal of Zheng Sheng College, in Cheung Chau - a school for young drug addicts - added: 'You can see that a high-handed approach hasn't been successful in curbing these activities, as they still come up so frequently. Substance abuse is considered a popular pastime in youth culture. The young people need education rather than punishment.'
Despite ketamine's upgrading to a dangerous drug, the amount seized has risen from 15.37kg last year to 32.01kg from January to August this year.
The Narcotics Bureau disagreed, saying the verdict would serve as an effective deterrent to youngsters.