A table of evidence was on display as Hong Kong police told a press conference they had arrest nine people on suspicion of terrorist activities.
They are the latest to be targeted under a sweeping national security law Beijing imposed on the financial hub last year.
Among them were six high school students. The police say members of the group had deliberately recruited them.
"They all have some planning at some stage to leave Hong Kong for good. So, the group is particularly interested in this group and recruited them to join the plot, to do the sabotage before their departures."
Those arrested also included a university management-level employee and a secondary school teacher.
It comes as Hong Kong’s leader Carrie Lam said on Tuesday (JULY 6) "ideologies" posed risks to national security.
Urging parents, teachers, and religious leaders to observe the behavior of teenagers and report those who break the law to the authorities.
Officers also froze bank funds and seized an explosive chemical from a hostel room police described as a laboratory for bomb-making equipment.
"They wanted to produce TATP (triacetone triperoxide) and use it to attack some of the public facilities in Hong Kong, including the cross-harbour tunnel, railways, court rooms, and even they wanted to lay the bomb in the rubbish bin on the street, with a view to maximise the damage caused to the society."
TATP has been used in attacks by extremists in Israel and London.
Beijing imposed the security law on Hong Kong last year, punishing what it regards as subversion, secession, terrorism and collusion with foreign forces with up to life in jail.
Authorities have repeatedly said it has "restored stability."