HONG KONG — The Hong Kong police have arrested four people over social media posts that called for the city to become independent from China, an early indication that the authorities will strictly enforce a new national security law and crack down on speech that is now considered illegal.
The sweep on Wednesday appears to be the first targeted arrests of activists under the new law, which came into force a month ago and gives the Chinese government broad new powers over the semiautonomous territory. It had already been cited in the arrests of about a dozen people during several demonstrations, including on July 1, the anniversary of Hong Kong’s return to Chinese control.
Human rights groups denounced those arrests, saying they showed that the authorities intended to use the new powers to clamp down on peaceful activities. The Wednesday arrests, rights groups said, sent another chilling message and raised concerns about a crackdown on activism and political speech in Hong Kong.
“The gross misuse of this draconian law makes clear that the aim is to silence dissent, not protect national security,” said Sophie Richardson, the China director for Human Rights Watch.
The police said the activists, three men and one woman whose ages range from 16 to 21, were arrested in the New Territories area of Hong Kong for the “publishing of content about secession, and inciting or abetting others for the commission of secession.” Officers seized mobile phones, computers and documents during the roundup.
Li Kwai-wah, a senior superintendent of the Hong Kong police’s new national security department, said the arrests were made after an organization posted on social media about creating a new party to promote Hong Kong independence. Its “declarations” referred to establishing a “Hong Kong country” and using “all means” to achieve its goals, Mr. Li said.
Mr. Li gave no further information about the organization or about the four people who were arrested. He said the comments had been posted after the security law took effect, but he would not say whether they had been taken down or elaborate further on their content.
A political organization called Studentlocalism said its former convener, Tony Chung, was among those arrested. When the national security law took effect, the group said it had ended its operations in Hong Kong but that some members would continue to work overseas.
Under the new law, Chinese security agencies can now operate openly in Hong Kong. But the Hong Kong police said the arrests on Wednesday had been carried out by its own national security department, not by Chinese security personnel.
The security law was imposed by Beijing after more than a year of large protests in Hong Kong, many of which involved violent clashes with the police. The protests were set off by a proposal to allow extraditions to mainland China from Hong Kong, which is guaranteed its own legal system under the terms of the former British colony’s return to Chinese rule in 1997.
The demonstrations evolved to encompass a range of issues, including the police’s use of force and calls for expanding direct elections.
The new law targets subversion, secession, terrorism and collusion with foreign powers, and many of its clauses indicate they were written to curb the protests. For a city that had generally had strong protections for free speech, the legislation represented a drastic shift.