HONG KONG (Reuters) – Hong Kong Broadband Network (HKBN) said on Thursday it has blocked a website that publishes material mainly on 2019 anti-government protests, to comply with the city’s national security law, marking the first censorship of a local website under the law.

While the internet in mainland China is heavily censored and access to foreign social media platforms and news sites is blocked, residents in Chinese-ruled Hong Kong have so far enjoyed greater freedoms under the “one country, two systems” framework.

“We have disabled the access to the website in compliance with the requirement issued under the National Security Law,” a spokesperson for internet service provider HKBN said in an email to Reuters, adding that the action was taken on Jan. 13.

The website, HKChronicles, first reported disruptions to its service last week.

On Sunday, the South China Morning Post newspaper, citing unnamed sources, reported that Hong Kong police had invoked the city’s national security law for the first time to block HKChronicles, which curates anti-government posts and publishes personal information on Hong Kong police officers. The news has caused concern among local residents and activists community.

Naomi Chan, editor of HKChronicles, said HKBN’s response had been expected and it would not affect operations. Efforts would continue to find ways to restore Hong Kongers’ access to the website, Chan said.

“This case represents a clear step towards the end of a relatively free and open internet in Hong Kong,” said Fergus Ryan, an analyst with the Australian Strategic Policy Institute.

Other major internet service providers in Hong Kong, China Mobile and PCCW, did not immediately reply to requests for comment by Reuters on Thursday afternoon.

HKBN did not comment on why HKChronicles faced issues last week.

The Hong Kong Security Bureau last week in an email declined to comment on specific cases but said the police “will act on the basis of actual circumstances and according to the law.”

The police did not respond to a request for comment from Reuters on Thursday.

The security bureau said offences endangering national security include secession, subversion, organisation and perpetration of terrorist activities and collusion with a foreign country or with external elements to endanger national security. The offences are punishable with up to life in jail, according to the security law.

“All relevant action will be taken strictly in accordance with the law,” a Hong Kong Security Bureau spokeswoman added.

Under the controversial security legislation imposed by Beijing on the Chinese-ruled city in June, the police can ask service providers to restrict access to electronic platforms or messages that could pose a threat to national security.

In mainland China, access to foreign social media platforms and news sites such as Facebook and the New York Times is blocked by what is called the Great Firewall, which filters and blocks traffic between Chinese and overseas servers.

Residents in Chinese-ruled Hong Kong, in contrast, have hitherto enjoyed freedoms unavailable on the mainland thanks to a “one country, two systems” framework that is meant to be valid until at least 2047.

Rights groups have voiced concern that the enactment of the national security law may herald the introduction of a censorship mechanism similar to the Great Firewall in Hong Kong.

“Closing this website represents another brick in the Great Firewall that Beijing is gradually building up around Hong Kong,” Ryan said.

Lokman Tsui, an assistant professor at the Chinese University of Hong Kong who specializes in privacy and online communications, said: “In the long term, it will push activism to go further underground, like people already switching to use Signal,” referring to a chat messaging app.

(Reporting by Hong Kong newsroom; Editing by Christian Schmollinger, Michael Perry and Hugh Lawson)