The Hong Kong government has cancelled the passports of six overseas-based activists under the new national security law, stepping up its crackdown on dissidents who moved abroad.

Those affected were former pro-democracy legislator Nathan Law, unionist Mung Siu-tat and activists Simon Cheng, Finn Lau, Johnny Fok and Tony Choi – all accused of endangering national security by the authorities.

The government said they have “absconded” to the UK.

Last year, police offered rewards of one million Hong Kong dollars (around £100,500) each for information leading to their arrests, drawing sharp criticism from Western governments.

According to the official statement, authorities also banned anyone from providing funds or economic resources to the six, leasing properties to them or forming any joint venture with them, among other restrictions. Doing so without authorisation would carry a penalty of up to seven years in prison.

The government said it acted because the six were continuing to engage in activities that endanger national security, smearing the city and colluding with external forces.

Secretary for Security Chris Tang said in a news briefing that some officials, politicians and media outlets in the UK have smeared the city’s government in an attempt to damage the rule of law in the financial hub, and tried to influence judicial decisions in some national security cases.

The six activists have been sheltered in the UK, Mr Tang said.

“We have to combat, deter and to prevent those people who have committed the offences relating to endangering national security through absconds,” he said.

Mr Tang, when asked whether subscribing to the activists’ accounts on Patreon and YouTube is illegal, said anyone who provides funds to them would be seen as violating the rules, regardless of the platform.

The measures were taken under the new powers granted by Hong Kong’s homegrown national security law enacted in March.

Beijing imposed a similar national security law on the territory in 2020 that has effectively wiped out most public dissent following the huge anti-government protests in 2019. Many activists were arrested, silenced or forced into self-exile.

But both the Chinese and Hong Kong governments insisted the law restored stability to the city after the protests.

More than 144,400 people from Hong Kong also have moved to the UK using a special visa that allows them to live and work in the country and apply for British citizenship after six years.

The UK introduced the pathway in 2021 in response to the 2020 security law.

Additionally, the British government granted asylum to activists Mr Law and Mr Cheng.

Mr Law said on Facebook he had submitted his passport to UK authorities when he applied for asylum in 2020 and has not collected it back, calling the government’s statement “a redundant move”.

But he urged people who remain in Hong Kong to prioritise their safety if the other restrictions under the new law worry them.

“Even if you cannot publicly support or discuss, please do not forget, do not lose your sense of justice,” he said.

Mr Lau said on X that he never owned a Hong Kong passport, so “it is ridiculous to cancel something that never exists”.

He said the latest measure is an act of transnational repression, but that it would not deter him from advocating for human rights and democracy.

Hong Kong’s political changes have long been a source of tension between the UK and the city government, as well as with Beijing due to the territory’s unique history as a former British colony that was returned to China in 1997.

Last week, two British judges confirmed they resigned from the city’s top court, with one citing as the reason “the political situation in Hong Kong”.

The other published a strongly worded article on Monday that said the rule of law in the city is in “grave danger” and that judges operate in an “impossible political environment created by China”.

That article drew swift criticism from the Hong Kong government.

In May, UK authorities charged three men with agreeing to engage in information gathering, surveillance and acts of deception that were likely to materially assist the Hong Kong intelligence service. One of the trio was later found dead in a park.

Chinese authorities in the UK and Hong Kong have decried the charges, saying they were the latest in a series of “groundless and slanderous” accusations that the UK Government has levelled against China.