A museum commemorating the deadly 1989 Tiananmen Square crackdown has been raided by Hong Kong police.
Officers were later seen carrying exhibits out of the June 4 Museum.
Four members of the group that ran the museum, the Hong Kong Alliance, were detained on Wednesday – including prominent pro-democracy activist and barrister Chow Hang Tung.
The arrests were made under the national security law, which has a maximum sentence of life imprisonment.
Police have accused Ms Chow of inciting subversion, her lawyers said.
The group, known for organising the city’s famed annual vigil for Tiananmen Square victims, denies accusations of being a foreign agent.
The museum was closed down by officials in June. Thursday’s raid was carried out by the newly created national security unit.
Among the exhibits seen being removed was a paper model of the Goddess of Democracy – a symbol of the 1989 pro-democracy student movement in Beijing.
Officers were also seen carrying out photos of the large candlelit vigils for Tiananmen victims.
The national security unit had earlier requested that the Hong Kong Alliance hand over information, reportedly including personal details of all members since the group’s founding and financial records.
On Tuesday, the deadline for the request, the alliance members handed over a letter explaining their refusal to co-operate.
The next morning, police officers arrested members of the alliance’s standing committee at their homes or offices.
Ms Chow, a human rights lawyer, was arrested earlier this year and charged with promoting unauthorised assembly. She was later released on bail.
She had been due on Wednesday to represent an opposition politician charged under the national security law at a bail hearing but was arrested at her office before she could appear in court.
China recently imposed a broadly worded national security law in Hong Kong that criminalises secession, subversion, terrorism and collusion with foreign forces.
Critics say it is aimed at crushing dissent but China says it is meant to maintain stability.