Hong Kong police, legal experts and lawmakers warned on Monday of a serious escalation in violence characterized by bomb plots that threaten the lives of residents — after more explosives were seized in Sai Ying Pun on Sunday night.

The police arrested 12 men and five women for their alleged role in three bomb plots and seized three half-made bombs that contained a total of 4.5 kilograms of explosives during citywide raids.

Briefing the media on Monday, Senior Superintendent Steve Li Kwai-wah said officers were tracking the source of these explosives — which included gunpowder and flammable metals.

"No civilized society with the rule of law can tolerate some of its people using bombs to coerce the government and other people to accept their views," stressed Li.

All of the 17 arrested, aged 21 to 53, were believed to be members of a social media group that had earlier claimed responsibility for three bomb plots targeting Caritas Medical Centre, Shenzhen Bay checkpoint and the Lo Wu railway station in January, as they demanded the government order a complete border shutdown with the Chinese mainland to curb the spread of the novel coronavirus.

Police said this situation is very worrying, as bombings no longer target only officers at public gatherings, but also civilians.

"Bombs are indiscriminate. Bombs cannot choose between a police officer and a child. There is no such thing as bombs targeting only the police," said Alick McWhirter, senior superintendent of the Explosive Ordinance Disposal Bureau.

Senior counsel and barrister Ronny Tong Ka-wah said police officers now were not the only target, because placing explosives in public spaces would risk hurting ordinary people.

"It is a terrorist attack if they want to achieve political goals by injuring civilians," said Tong.

Echoing Tong's concerns, Barrister Lawrence Ma Yan-kwok, chairman of the Hong Kong Legal Exchange Foundation, told China Daily that the 17 arrested people could be terrorists if it is proved that their possession of explosives is part of a scheme to push their political agenda.

"There is a current tide of international terrorism where people in the last decade are prone to use violence and illegal means to achieve a certain political aim. Hong Kong is not immune to this tide," said Ma.

The city's largest party in the legislature, the Democratic Alliance for the Betterment and Progress of Hong Kong, condemned localist radicals for "plotting serial bombings and advocating terrorism" for their own political ends.

The party also noted that some residents and "self-claimed district councilors" had tried to obstruct police operations by creating disturbances and disrupting elevators in buildings by triggering fire alarms.

Police confirmed one of their raids to find explosives in Tai Po was impeded by a district councilor, and some residents besieged officers as they escorted a suspect.