Police in Hong Kong on Tuesday added to a wanted list six people deemed to have violated the national security law aiming at cracking down on anti-government activities.

The six include Chung Kim-wah, the former executive of a think tank -- the Hong Kong Public Opinion Research Institute.

Chung was known as a pro-democracy advocate critical of the government. He moved to Britain in 2022 to seek freedom of speech.

The police said at a news conference that Chung advocated for Hong Kong independence and incited secession through social media posts, without specifying what remarks and actions were suspected to be illegal.

The national security law, which took effect four years ago, covers activities outside Hong Kong.

Many pro-democracy activists have moved overseas since the introduction of the law, as authorities are tightening their crackdown in the territory.

Aside from the six people, more than 10 activists living abroad have already been put on a wanted list.

Agnes Chow is among them. She is a prominent figure in Hong Kong's pro-democracy movement and has also spoken in Japanese to call for support for the movement. She is currently staying in Canada.