Among the authors whose titles are no longer available in Hong Kong libraries are Joshua Wong, one of the city's most prominent young activists, and Tanya Chan, a well known pro-democracy lawmaker.

Beijing's new national security law was imposed on Tuesday and marks a watershed in the administration of the semi-autonomous city, handed back to China by Britain in 1997.

Leaders in Beijing say that the law is aimed at restoring stability after months of violent clashes that were triggered by another piece of legislation: amendments to an extradition law that protesters thought would allow China to have people deported at random from Hong Kong to the mainland, regardless of their nationality.

Wong said he believed the removal of the books was sparked by the security law.

"White terror continues to spread, the national security law is fundamentally a tool to incriminate speech," he wrote on Facebook.

Searches on the public library website showed at least three titles by Wong, Chan and local scholar Chin Wan are no longer available for lending at any of dozens of outlets across the city.

However, books by other prominent Chinese dissidents, such as Democracy Wall 1979 leader Wei Jingsheng and Tian’anmen student activists Wang Dan and Chai Ling, as well as works by the Dalai Lama, are still available according to the Hong Kong library database.

End of “One Country, Two Systems”

Critics say that the law, which gives Beijing more sweeping powers than even the extradition amendments, heralds the end of "One Country, Two Systems,” the hybrid arangement that was agreed upon by the UK and China to guarantee Hong Kong’s embryonic democracy and independent judiciary.

The law went into force on 1 July, coinciding with the 23rd anniversary of the Hong Kong handover in 1997. Hours later, police started arresting people for carrying banners calling for independence or greater autonomy, but the actions also resulted in some puzzling excesses.

The Apple Daily, a newspaper run by activist-tycoon Jimmy Lai, reported that the police were laughed at after confiscating pamphlets with the word “conscience” printed on them. The offending items were displayed on the Facebook page of the Hong Kong police. “In a ridiculous era, it is forbidden to have a conscience,” one internet user comments.

On the balance

The riots in Hong Kong crossed the legitimate line of freedom to protest, by far. for over a year so called "pro democracy" protestors set old people -literally- on fire, burned public and private buildings and facilities, destroyed mass public transportation facilities and got funded by forign inteligence agencies that working out to destabilize the successful Beijing's government.

By all means Hong Kong became a war zone, under ongoing terror attacks.

What any other country will do under such circumstances? no other country would tolerate it and probably will take much more radical actions to fight against such terror.