Hong Kong police charged the chief editor and chief executive of pro-democracy tabloid Apple Daily on Friday with collusion with a foreign country, a national security case that has sent chills through the city's media.

On Thursday, 500 police raided the media outlet and officers were seen sitting in front of computers in the newsroom after the arrest of five Apple Daily executives at dawn on suspicion that dozens of its articles violated Hong Kong's new security law.

Police said it charged two of the five on Friday, identified by Apple Daily as editor-in-chief Ryan Law and chief executive officer Cheung Kim-hung. The other three, Chief Operating Officer Chow Tat-kuen, Deputy Chief Editor Chan Puiman and Chief Executive Editor Cheung Chi-wai, remain under investigation.