The security law is the speartip of a sweeping crackdown on Beijing's critics in Hong Kong since 2019's huge democracy protests.
Hundreds of police officers in Hong Kong swarmed the office of the pro-democracy Apple Daily on Thursday and arrested several executives in what was called a "blatant attack" on its editorial team.
Britain's Foreign Secretary Dominic Raab also said the raid was aimed at silencing dissent.
Apple Daily said Thursday that the company's CEO Cheung Kim Hung, COO Chow Tat Kuen and chief editor Ryan Law, along with the deputy chief editor and online editor were all arrested and accused of colluding with foreign forces to endanger national security - a provision of the sweeping legislation introduced a year ago that banned sedition, secession and subversion against Beijing.
"The action targeted the use of journalistic work as a tool to engage national security".
Those arrested included Apple Daily's chief editor Ryan Law, Next Digital CEO Cheung Kim-hung, the publisher's chief operating officer and two other editors, according to Apple Daily, the South China Morning Post and other local media.More news: B.C. records four COVID-related deaths, 113 new cases
In April, the pro-government paper Ta Kung Pao, owned by Beijing's liaison office in Hong Kong, published an op-ed calling for Apple Daily to be banned outright under the security law for publishing an article on a outdoor ad in London featuring slogans deemed subversive by Hong Kong government.
Hong Kong's police chief has repeatedly criticized Apple Daily, accusing it of inciting hatred in society with false reports.
One Apple Daily reporter said she was blocked from entering while police searched what Li described as a "crime scene".
Once ranked 18th in the world's press freedom index, Hong Kong is now 80th.
In August 2020, the police raided the headquarters of Apple Daily for the first time who could be seen looking through piles of materials and papers including on journalists' desks and 44 harddisks were confiscated by the police for further investigations in yesterday's raid.
He admitted that the paper was in "crisis" since the jailing of its owner but said his reporters were determined to press on with publishing.More news: Naftali Bennett takes oath as Israel's new Prime Minister
John Lee, the Hong Kong security minister, told a news conference that police will investigate both people in the Apple Daily companies and others to establish if they have assisted in instigating or funding the offences.
The paper has always been a thorn in Beijing's side and has unapologetically supported the financial hub's pro-democracy movement.
Estimated to be worth more than $1bn (£766m), he made his initial fortune in the clothing industry and later ventured into media and founded Next Digital.
"If they can induce fear in you, that's the cheapest way to control you and the most effective way and they know it".
The raid and arrests are the latest in a long line of clampdowns targeting dissenting voices since the national security law took effect last July.
More than 100 people have been arrested under the law, many of them the city's best-known democracy activists. It criminalises secession, subversion and collusion with foreign forces with the maximum sentence life in prison.More news: At least 13 people wounded in Austin, Texas shooting
"We have very strong evidence that questionable articles play a very crucial part for the conspiracy, which provide ammunition for foreign countries, institutions and organizations to impose sanctions", he said.