Investigators said they raided a hotel room in Hung Hom on Friday and found almost seven kilograms of heroin and 13 kilograms of ketamine inside.
A 17-year-old boy was arrested at the scene.
The force said further investigation led them to a factory building unit in Tsuen Wan on the same day, where officers arrested three other suspects aged between 16 and 20.
“The police have noticed that because of the pandemic and the approaching summer vacation, most teenagers and students don’t have to go to school. Drug traffickers have made use of this chance to lure our young people with offers of quick money, taking advantage of their weakness being immature,” said senior inspector Chan Chi-wa of the Narcotics Bureau during a press briefing.
Separately, a 39-year-old man was arrested after he was caught carrying more than 900 grams of cocaine during a stop-and-search in Wong Tai Sin.
Police estimated the seized cocaine to worth about HK$3.5 million.
They said officers also found drug-making tools at the man’s rented home.