China‘s national security authorities in Hong Kong and the city’s police launched their first publicly known joint operation, raiding the homes of six people on suspicion of colluding with foreign forces to endanger national security.

The police’s statement on late Thursday did not disclose the identity of the six people suspected of breaking the 2020 Beijing-imposed national security law between November 2020 and June 2024. Beyond their homes, officers searched the office of the organization involved and seized exhibits such as bank documents and devices for further investigation, according to the statement. The six people were required to surrender their travel documents.

Beijing‘s national security arm in Hong Kong also had requested assistance from the city’s national security police, including in arranging interviews with the people in the case, the police said. But the local force did not elaborate details of their accusations and which organization it was, saying the investigation was still underway.

Since the 2020 security law took effect, many leading activists have been prosecuted or jailed for national security offenses . Last week, prominent young activist Joshua Wong, who was already convicted and sentenced over a subversion case last year, was charged for the second time under the law. He faces up to life in prison over the fresh charge of conspiracy to collude with foreign forces to endanger national security.

The Beijing and Hong Kong governments insist the law was necessary for returning stability to the city following massive anti-government protests in 2019.

In May, Hong Kong enacted subsidiary legislation for a separate, homegrown national security law, which was passed last year. The subsidiary legislation requires public servants, if requested, to provide all necessary and reasonable assistance to Beijing’s national security office in Hong Kong. Local public servants must offer such help if the office needs to ascertain whether a case involves a special circumstance that could allow it to have jurisdiction over the case.

Over the past week, the Hong Kong authorities have stepped up their national security work as the fifth anniversary of the enactment of the Beijing-imposed law neared, including targeting a mobile game application which they accused of advocating armed revolution and promoting secessionist agendas.