HONG KONG (NYTIMES) - Hong Kong's biggest mobile telecoms companies appear to have severed access to a website that listed the personal information of police officers, setting off fears that the authorities may use a new national security law to adopt censorship tactics widely used in mainland China.

Users attempting to access the site, called HKChronicles, on their mobile devices first noticed the disruption last Wednesday evening (Jan 6), according to the site's owner Naomi Chan, an 18-year-old high school student. Disruption came without any warning or explanation, she said.

A New York Times analysis confirmed that the problem accessing the site comes from the telecoms service providers. At least some people in Hong Kong were still able to reach the site through their home or office Internet connections.

The police in Hong Kong declined to comment on the disruption but insisted they had the power under the new national security law to block access to information online.

In a statement, the police said they "can require service providers to take restrictive actions against messages posted on digital platforms, which likely constitute the offense of endangering national security or incite a national security offence".

The disruption raised the prospect that the city, long a bastion of online freedom, could begin to fall under the shadow of the tight censorship system that separates mainland Chinese Internet from the rest of the online world.

On Hong Kong social media, many people worried that the authorities could eventually bring the city's overall access to the open Internet to an end.

"Their talking point has been the national security law will only target a small group of people," said Assistant Professor Lokman Tsui from the Chinese University of Hong Kong who specialises in online communication.

Since the law went into effect over the summer, however, Hong Kong authorities have cited the law to arrest growing numbers of pro-democracy activists and politicians and well as a high-profile newspaper publisher.

"In practice, it hasn't been limited to a small group of people," he said. "My concern is that Internet censorship similarly won't be limited to a small group of websites."

The national security law, which empowers police to censor and use invasive surveillance tactics, has already constricted online life in Hong Kong. Police have hung a camera outside the house of one prominent politician, broken into the Facebook account of another and demanded passwords and fingerprints from the people they arrest to get access to their phones.

Caught in the middle, major American technology companies like Google said they no longer accept user data requests from Hong Kong authorities, though the law could punish refusals with jail time for employees. Many in Hong Kong have switched to encrypted chat apps and scrubbed social media accounts of posts they worry could bring new police attention.

"Today it's HKChronicles - would it be foreign media or local media tomorrow?" said Ms Glacier Kwong, of Keyboard Frontline, a non-governmental organisation that monitors digital rights in Hong Kong. "Would Telegram and Signal be the next ones? The government can do whatever they want with the national security law, and Hong Kong can easily become another Chinese city behind the Great Firewall."

HKChronicles was inspired by the pro-democracy protests of 2019, which shook Hong Kong and prompted mainland Chinese officials to eventually crack down. As images of the violent tactics of police began to spread around the world, many police stopped wearing identifying markers.

In response, protesters began to share information online to identify and sometimes harass them. The HKChronicles listed the personal information of about 1,500 police officers and another 1,000 pro-Beijing supporters.

The Times attempted to connect to hkchronicles.com on three different Hong Kong Internet service providers. Each attempt failed, though in a different way.

That suggested to experts that the blockage was deliberate. If it were an error, the disruptions would look the same.

"None of this is a misconfiguration mistake," said Mr Ben April, the chief technology officer at Farsight Security, an Internet security firm that specialises in what is called the domain name system, or DNS, which acts as a sort of phone book for the Internet. "There is no typo that can cause this."

At one Internet provider, China Mobile Hong Kong, the disconnection - of a type known as a drop action - indicates direct involvement by the telecoms company. "A drop action is a specifically configured element of a DNS firewall environment," Mr April said. "This is not something the owner could have configured, intentionally or accidentally."

China Mobile Hong Kong, an arm of China Mobile, the Chinese state-run company, declined to comment. Two others tested by the Times, SmarTone and Hutchison Telecommunications, which are controlled by local conglomerates, did not respond to e-mailed requests for comment.

Users of PCCW, another locally owned carrier, told The Times their access to the site was blocked, too. A spokesman declined to comment.

The Hong Kong blockages are "really easy to circumvent and clumsy", said Asst Prof Tsui. Still, he said, the authorities may not want to control the Internet as tightly as Beijing for fear of scaring off the global banks and international companies that have made the city their Asian headquarters.

"They want the city to be one that can make money and have the financial flows, and the Internet is important for that, so they have to get the balance of censorship and surveillance right," he said.