It was passed in just six weeks, skipping Hong Kong’s fractious legislature, and the precise wording was kept secret until it came into effect late Tuesday.
It outlaws subversion, secession, terrorism and colluding with foreign forces to undermine national security, with sentences of up to life in prison.
It also topples the legal firewall that has existed between the city’s judiciary and the mainland’s party-controlled courts.
China will have jurisdiction over “serious” cases and its security agencies will also be able to operate publicly in the city for the first time.
Another provision also claims universal jurisdiction for national security crimes committed beyond Hong Kong or China.
Authorities in Taiwan opened a new office to deal with Hong Kongers seeking refuge.
Beijing says the law will not end Hong Kong’s freedoms but critics have little faith in those assurances, given how similar national security laws are routinely used on the mainland to crush dissent.
by Yan ZHAO / Jerome TAYLOR