The sweep comes after a major rally planned for Saturday was banned by police on security grounds, and then called off by the organisers.
The latest protest had been due to mark the fifth anniversary of Beijing’s rejection of a call for universal suffrage in the semi-autonomous city, sparking the 79-day Umbrella Movement in 2014.
Hong Kong has been locked in three months of political crisis, with increasingly violent clashes between police and protesters that have prompted an escalating intimidation campaign from China.
Two of the Umbrella Movement’s leaders, Joshua Wong and Agnes Chow — both still well-regarded among the city’s youth — appeared in court accused of “inciting others to take part in unauthorised assembly” among other charges, having been arrested in dawn swoops on Friday.
After receiving bail, they spoke outside the court and Wong vowed to “continue our fight”, railing against the “chilling effect” of the arrests on opponents of Hong Kong’s Beijing-backed government.
Authorities are “trying to create white terror” to scare people away from participating in the social and democratic movement, he added — deploying a term used for China’s efforts to fragment and harass the protesters.
“My arrest shows the government answers our request for a dialogue with batons, tear gas, rubber bullets and mass arrest,” he tweeted.
