The southern Chinese city's security police said 19 activists "organised, established or participated in a subversive organisation called the Hong Kong Parliament", referring to a pro-democracy NGO established in Canada.

The police accused the group of seeking to "overthrow and destroy" China's fundamental system of government "by unlawful means".

A reward of HK$200,000 ($25,500) each was offered for 15 of the activists, while the four others were already wanted for HK$1 million, the police said in a statement.

As of July 1, Hong Kong authorities had arrested 333 people for alleged national security crimes, with 165 convicted in Hong Kong.