Sunday marks four years since China's national security law for Hong Kong went into effect. The legislation is designed to crack down on anti-government activity.
The suppression of free speech intensified this year after a local ordinance to complement the law came into force in March.
The security legislation took effect on June 30, 2020, about a year after massive dissident protests erupted in Hong Kong.
Under the law, pro-democracy politicians and activists have been arrested, and anti-government rallies and demonstrations have been restricted.
Last month, 14 pro-democracy activists were convicted for their alleged violation of the law. They are among 47 activists, including former pro-democracy legislators, who were charged with subversion three years ago.
Court proceedings continue for the other defendants, effectively extending their detention.
A local ordinance that took effect in March criminalizes espionage and interference by foreign entities. It also stipulates stricter punishment for acts that instigate hatred against the Chinese government.
Earlier this month, a man was charged with violating the law for allegedly wearing a T-shirt with a slogan used in the 2019 protests.
Hong Kong's security authorities told NHK that over the past four years 299 people have been arrested for allegedly endangering national security.