A police agent went undercover as a gangster for nine months to help bust two factions of the Wo Shing Wo triad and arrest 63 people, police said.
The arrests included 16 secondary school pupils, with the youngest just 13 years old.
The undercover operation, codenamed "Highscorer", produced a list of 80 triad members with evidence of their illegal activities, Senior Superintendent Au Chin-chau of the New Territories South regional crime unit said yesterday.
"Police believe the operation has smashed two triad gangs and successfully cracked their illegal activities," he said.
An initial investigation indicated both factions were active in Kwai Chung and Tsim Sha Tsui, police said. The Kwai Chung gang was understood to have recruited youngsters to push illegal drugs and extend its influence in recent months.
An undercover policeman infiltrated the gang in June to collect evidence and identify active members.
At about 11pm on Thursday, more than 100 officers started to raid entertainment venues and residential flats across the city. Police nabbed 43 men and 20 women, aged between 13 and 43. They also seized a small quantity of illegal drugs.
Among the detainees, 17 people were picked up from a pub in Kwai Chung on Thursday night as they met to discuss retaliatory action against a rival gang.
"Police received a tip-off that indicated triad members were using the excuse of holding an Easter party to cover up their triad meeting," Au said.
Officers caught 11 others at a nearby park and cybercafe where they were known to gather. Seven water pipes were seized.
At the same time, police raided a nightclub and a pub in Tsim Sha Tsui where a man and two women were arrested. The women, who were hostesses at the nightclub, were accused of pushing illegal drugs to their clients.
The 63 suspects were arrested for offences including claiming to be triad members, recruiting others into triads, criminal damage, criminal intimidation, wounding and possession of offensive weapons, and drug trafficking.