Hong Kong's national security police arrested 11 people in dawn raids on Thursday, including a veteran human rights lawyer, on suspicion of helping a group of activists make a failed bid to flee the city by speedboat.
"Eleven people were arrested by the national security department for 'conspiracy to assist offenders'," a senior police source told AFP.
The officer confirmed those arrested were suspected of aiding 12 Hong Kong pro-democracy activists caught last August by Chinese coastguards as they tried to flee by boat to Taiwan.
Those on board were facing charges in Hong Kong for crimes linked to huge and often violent democracy protests that convulsed the finance hub in 2019.
The arrests come a week after national security police detained more than 50 of the city's most prominent democracy activists for subversion, one of the new crimes listed in a sweeping national security law that Beijing imposed on the city last year.
Among those detained on Thursday was Daniel Wong, a veteran human rights lawyer and an outspoken supporter of Hong Kong's democracy movement.
Willis Ho, a former student leader, confirmed her mother was among those arrested.
Last month a Chinese court jailed 10 of the 12 fugitives for up to three years for "organising and participating in an illegal border crossing".
Two teenagers were returned to Hong Kong to face charges including attempted arson and possession of offensive weapons.
The national security law mandates up to life imprisonment for any offence China views as "secession, subversion, collusion with foreign forces and terrorism".
At least 90 people have been arrested since the law's enactment, including US-born human rights lawyer John Clancey, prominent activist Joshua Wong and pro-democracy media mogul Jimmy Lai.
First website takedown
Meanwhile, a Hong Kong internet provider said on Thursday it had blocked access to a website following a police order, the first confirmed takedown using the national security law.
Unlike mainland China, Hong Kong has open internet access, but critics of Beijing fear powers given to the police under the new law could herald the end of that freedom.
Internet users noticed the website HKChronicles was unreachable from some Hong Kong-based devices last week, and its owner put out a statement saying she believed authorities were blocking access.
Police declined to comment, but on Thursday Hong Kong Broadband Network - one of the city's internet service providers - confirmed a takedown order had been issued.
"We have disabled the access to the website in compliance with the requirement issued under the National Security Law," the company said.
HKChronicles, which is still available overseas and in Hong Kong through virtual private networks, is a controversial site.
It ran lists of businesses that support the democracy movement, and collected stories and footage from huge and often violent pro-democracy protests that swept Hong Kong in 2019 - with a particular focus on allegations of excessive police violence.
But after officers began removing identifying badges during clashes with protesters, the website started collecting their personal details - a tactic known as doxxing, which is illegal in Hong Kong and many other jurisdictions.
It also listed the names and details of many pro-Beijing figures.
Similar websites doxxing pro-democracy supporters also exist.
Access to the internet in authoritarian China is impeded by a "Great Firewall" that limits sites and information that people on the mainland can access.
China also employs a sophisticated censorship network which scrubs posts deemed sensitive from the digital world.
But semi-autonomous Hong Kong remains outside that firewall, a crucial component of its status as an international business hub.
The new national security law includes fresh police powers to order internet providers to remove websites or content deemed to breach national security, sparking fears the "Great Firewall" might be widened to one day encompass Hong Kong.
