HONG KONG — Hong Kong’s national security police arrested six people linked to Stand News, an independent online media outlet, in another sign that the city’s once-thriving press freedom is taking a turn for the worse.

Around 200 officers also raided the Stand News office, with a search warrant under the national security law, allowing them to “search and seize relevant journalistic materials.”

The arrests came about six months after the pro-democracy paper Apple Daily was forced to shut down following a newsroom raid, seizure of its assets, and arrest of its founder, Jimmy Lai.

Those arrested on Wednesday included former Stand News board members Denise Ho, a well-known pop singer and democracy activist, and Margaret Ng, an ex-lawmaker. Ronson Chan, deputy assignment editor and Hong Kong Journalists Association chairman, was also detained.

The arrests were made at their homes under a colonial-era law covering conspiracy to print or distribute seditious materials, police said in a statement. Chan attempted to live-stream police arriving at his door.

“Anyone who use journalism as a disguise and a tool to carry out acts that endanger national security will be severely struck by the SAR government,” said Chief Secretary John Lee.

The HKJA in a statement posted on Facebook said it is “deeply concerned that the police have repeatedly arrested senior members of the media and searched the offices of news organizations … HKJA urges the government to protect press freedom in accordance with the Basic Law.”

Police were seen carrying boxes out of the Stand News office.