Activists of the Hong Kong Alliance in Support of Patriotic Democratic Movements of China said Thursday that they had received a notice issued by the city's police commissioner Friday last week that said the group must take down all its online content within seven days, in order to comply with the national security law, reports Kyodo News agency.

The Alliance has since closed its website, which had a large amount of content about the 1989 Tiananmen Square protests, including photos of the protests and documented testimonies by families of some of the protesters killed in the crackdown, the news agency reported.

The group also deleted accounts of social media platforms including Facebook, Instagram, Twitter and YouTube.

The group said that it is going to disseminate information by creating a new Facebook page.

Four members of the group, including vice chairwoman Tonyee Chow, were arrested earlier this month after they refused to comply with a police demand to hand in information on its operations, Kyodo News reported.