Protesters planned to gather at the city's Legislative Council during a debate on a related law which would criminalize insulting China's national anthem - though security forces stopped them before they could get that far.
Riot police fired pepper pellets to disperse crowds in the heart of the financial district and elsewhere, while groups of suspected protesters were gathered up and made to sit on sidewalks as their belongings were searched, according to Reuters.
"Hong Kong independence, the only way out!" chanted protesters, along with "Liberate Hong Kong! Revolution of our times" - which is exactly what CCP officials warned about while justifying the new laws which include provisions against secession, subversion and foreign interference.
One protester had a sign reading "one country, two systems is a lie."