Hong Kong Police Wanchai district headquarters, Aug 21, 2019 Photo: Xinhua

The Hong Kong Police Force (HKPF) announced on Tuesday that they have arrested nine suspects under the national security law for Hong Kong who attempted to make bombs and planned a series of attacks.

The nine are suspected to have engaged in a terrorist activity. They had previously made bombs in a hostel and planned to bomb courts, cross-harbor tunnels and railways and even planned to put some of these explosives in trash bins on the street to "maximize damage caused to the society," the HKPF said in the announcement. 

They are five men and four women aged between 15 and 39 years old. Six of them are secondary school students, one secondary school teacher and a university management-level employee, authorities said. Police said the group belongs to a secessionist organization called "Returning Valiant."

The HKPF has dismantled the explosive lab, which was located in a hostel room. Officers also froze bank funds of around HK$600,000 ($77,238), as well as cash that they believed was linked to suspected terrorist activities.

Chief Executive of the Hong Kong Special Administrative Region Carrie Lam noted that the implementation of the national security law has effectively stopped violence and chaos in the past year, yet there is still a shadow of black violence in the city.

"The lack of supervision of social networks has been taken advantage of by some people to spread hateful ideology and extremist ideas," Lam pointed out on Tuesday. She noted that a few recent violent incidents have sounded the alarm.

On Thursday, a man stabbed a police officer in the street and later killed himself in a lone-wolf style terrorist attack. The 28-year-old officer sustained a punctured lung in the attack and remains in a hospital, according to local media. The case was taken over by the national security department.

On the same day, bottles of combustible material were thrown onto a slope near the Government House and two were arrested in the case. 

Such actions prove that "black violence" has gone from being public to being covert, Lam said. 

The national security law for Hong Kong has been in effect for over a year, during which time over 120 people have been arrested under the law. 

Experts noted that the law has generally restored the stability of Hong Kong society, although a few isolated, vicious cases still exist. 

"All government departments shall have a sense of national security, including education, broadcasting, and culture and the arts," Lam said. "The public shall openly condemn violence, and it shall not find excuses for the perpetrators of violence."

Fan Peng, a research fellow at the Chinese Academy of Social Sciences' Institute of Political Sciences in Beijing, pointed out that some extremist secessionist forces have infiltrated the schools in the past few years, leading to irrational incitement of youth as well, a long-standing public safety concern. 

"This phenomenon is expected to be tackled as the national security law further takes root in the minds of the public," Fan noted.

A recent poll shows that over 70 percent of Hong Kong residents understand and support the national security law, which shows the law has taken root in society. 

"The national security law has served as a very good legal education and reshaping of legal authority for Hong Kong society. More and more people are aware of the legitimacy and necessity of the national security law," said Tian Feilong, associate professor at Beihang University in Beijing and a member of the Beijing-based Chinese Association of Hong Kong and Macao Studies.