Friday marks three years since China's national security law for Hong Kong went into effect, designed to crack down on anti-government moves.

The legislation took effect on June 30, 2020, about a year after massive dissident protests erupted in Hong Kong.

Under the new law, pro-democracy politicians and activists have been arrested, and anti-government rallies and demonstrations have been restricted.

People have been charged if their words or online messages are deemed as fomenting hatred against the government or instigating Hong Kong's independence.

In March, a woman was arrested in Hong Kong when she briefly returned home from Japan where she was studying. She was alleged to have posted messages online inciting Hong Kong's independence.

Local media said it was the first case that the law was applied to activities outside Hong Kong.

The Hong Kong government is calling on residents to report to authorities any possible violations of the law.

Police there say they have received more than 500,000 tip-offs from the public.

Tightened restrictions on free speech are believed to have partly contributed to people's exodus from the territory. The Hong Kong government says about 60,000 citizens have left for work or study overseas in 2022 alone.