Hong Kong authorities have arrested and charged most of the city's pro-democracy advocates, including Joshua Wong, a student leader during 2014 protests.
China says the security law was needed to return stability to the global financial hub.
In an interview with AFP last month, chief editor Law struck a defiant tone.
Those arrested included Next Digital Chief Executive Officer and Apple Daily publisher Cheung Kim-hung and Chief Operating Officer Royston Chow, as well as the paper's Editor-in-Chief Ryan Law and deputy editors Chan Pui-man and Cheung Chi-wai.
National security police arrested the editor and four other directors of Apple Daily on Thursday morning and raided the pro-democracy media group's offices in Tseung Kwan O for the second time in a year to execute a warrant.
Hong Kong Security Minister John Lee told a news conference that police will investigate those arrested and others to establish if they have assisted in instigating or funding the offenses.
"Hong Kong has been left with little free speech under the NSL (national security law), which aims to silence all dissent".
Lee went on to say that "normal journalistic work takes place lawfully and freely in Hong Kong", adding that the suspects used journalism to "further their criminal activities".
Choy is a freelance producer with local public broadcaster Radio Television Hong Kong (RTHK), who was found guilty and fined by the Hong Kong government in April for making false statements to obtain vehicle records, which were used in her documentary examining a mob attack on commuters at a Hong Kong metro station on July 21, 2019.
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The security law introduced last June is the speartip of a sweeping crackdown on Beijing's critics in Hong Kong since 2019's huge democracy protests.
A police source confirmed to AFP that all five were executives from Next Digital, Apple Daily's parent company.
Apple Daily cited a government statement on the raid, which said that the operation was conducted "with a search warrant under Article 43 (1) of the national security law, which "covered the power of searching and seizure of journalistic materials".
According to the report, the officers accessed the computers of the staffers and requested that everyone register with their identity cards, staff ID and personal information before they enter, while not allowing the journalists to return to their desks. It punishes anything Beijing deems as subversion, secessionism, terrorism and collusion with foreign forces with up to life in prison.
Trading in the shares of Next Digital was halted Thursday morning, according to a notice on the Hong Kong stock exchange.
Police said the five executives were arrested for collusion with a foreign country or external elements "to endanger national security".
Media freedom in Hong Kong has deteriorated in recent years, with increased censorship at the city's once outspoken public broadcaster RTHK.
Police said they had evidence that more than 30 articles published by Apple Daily played a "crucial part" in what they called a conspiracy with foreign countries to impose sanctions against China and Hong Kong.
China's Hong Kong Liaison Office said on Thursday it firmly supported what it described as the "just action" of the city's police. It is unclear whether Apple Daily will now be able to pay its staff.
In a letter to readers after the raid, Apple Daily vowed to continue publishing with a clear conscience. "Authoritarianism is waging a brutal war on @appledaily_hk, a desperately endangered symbol of freedom in #HongKong", he tweeted from his official account, "I'm out of words to describe my anger & sadness at witnessing this tragedy".