Hong Kong's Security Bureau said on Wednesday it would use powers in a new national security against six exiled activists residing in Britain, including cancelling their passports, after they fled the China-ruled city, Paralel.Az reports citing Reuters.

The six are Nathan Law, Christopher Mung Siu-tat, Finn Lau, Simon Cheng, Johnny Fok Ka-chi and Tony Choi Ming-da. City authorities put them on a wanted list last year.

"These lawless wanted criminals are hiding in the United Kingdom and continue to blatantly engage in activities that endanger national security," the bureau said in a statement.

"They continue to collude with external forces to protect their evil deeds. We therefore have taken such measures to give them a strong blow," it added, noting that these moves involved exercising powers in a new set of national security laws known as Article 23, which were enacted in March.

Hong Kong authorities have outlawed more than a dozen overseas activists based in the United States, Britain and other countries. A bounty of HK$1 million ($128,000) for information for these activists was also offered.

The new measures for the six in Britain prohibits providing them with funds and cancels their business dealings in Hong Kong. The new security bill includes punishments for offences including treason, sabotage and sedition.

Security chief Chris Tang called the measures against the activists "a necessary action" at a news conference on Wednesday.

The Article 23 laws come on top of a sweeping China-imposed national security law in 2020 that has been used to jail pro-democracy activists, as well as shutter liberal media outlets and civil society groups.

Crimes such as subversion, collusion with external forces, sedition, theft of state secrets and espionage now carry jail terms of several years to life.

The United States, Britain and Australia, where some of these activists are now based, have criticised the national security laws as a tool to silence dissent.

Hong Kong and Chinese authorities, however, say the laws are necessary and have restored stability since mass pro-democracy protests in 2019.