Media tycoon Jimmy Lai and six others were arrested Monday on suspicion of violating the new Chinese security law.
71-year-old Lai and the others are suspected of conspiring with foreign powers. It is expected that a dozen more people will be arrested on the same suspicions on Monday.
Lai is the founder of Apple Daily newspaper, a prominent Hong Kong democracy activist and critical of Chinese rule in Beijing. In April he was also arrested on suspicion of organizing and participating in "illegal meetings".
This is the most prominent arrest since the introduction of Hong Kong's new security law on July 1. The law allows China to crack down on opposition politicians and activists. Hundreds of arrests have been made since then.
Several countries have suspended their extradition treaty with Hong Kong because of the law. The US also stopped the preferential treatment Hong Kong received from the country and imposed sanctions on Carrie Lam, the leader of Hong Kong.
See also: Four questions about Hong Kong and the new Chinese security law