HONG KONG (AP) — Hong Kong police on Tuesday said they arrested nine people on suspicion of engaging in terrorist activity, after uncovering an attempt to make explosives and plant bombs across the city.

Of the nine arrested, six are secondary school students, police said. The group were attempting to make the explosive triacetone triperoxide (TATP) in a homemade laboratory in a hostel.

Police said they planned to use the TATP to bomb courts, cross-harbor tunnels in the city, railways and even planned to put some of these explosives in trash bins on the street “to maximize damage caused to the society.”

The nine arrested were between 15 and 39 years of age and are five men and four women, according to Senior Superintendent Li Kwai-wah of the Hong Kong Police National Security Department.