Hong Kong media mogul Jimmy Lai, activist Agnes Chow and eight others were arrested Monday for alleged breaches of the sweeping national security law recently imposed by China.

The arrest of Lai, one of the most famous democracy activists and critics of the Chinese Communist Party in Hong Kong, is the highest-profile police operation yet using the security law, which entered into force in the territory on June 30.

Hong Kong media tycoon and founder of Apple Daily newspaper Jimmy Lai arrives at the West Kowloon Magistrates' Court on May 18, 2020 in Hong Kong, China.(Getty/Kyodo)

The Apple Daily, founded by Lai, said police detained Lai and his two sons along with publisher Cheung Kim-hung, three other senior executives of the newspaper and two other activists. Lai was handcuffed while being taken away from his residence by police, according to the newspaper.

One of the sons was arrested on suspicion of collusion with foreign and external forces to endanger national security, and the other was detained for conspiracy to defraud, local media TVB reported.

"Jimmy Lai is being arrested for collusion with foreign powers at this time," the group's executive and Lai's top aide Mark Simon, who is not in Hong Kong and wanted by police, tweeted.

Some 200 police officers later searched the daily's headquarters, with Lai and Cheung present, media footage showed.

"Of course, press freedom is being infringed," Lai told the daily's reporter in response to his arrest while being escorted away by police inside the daily's headquarters. "There is nothing I could be worrying about, come what may."

Chow was arrested late Monday at her home for allegedly inciting secession, according to her Facebook posts.

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Steven Li of the police's national security unit set up to enforce the law said late Monday that five men and a woman were suspected of financing and organizing lobbying for foreign sanctions on Hong Kong, which constitute breaches of the security law.

"The activities have been continuing after the law took effect (on June 30)," Li told reporters. He added that two of the men and four others were also accused of conspiracy to defraud.

While stressing that police had left news materials untouched during the raid at the media office to show respect for press freedom, Li said the arrests were not made in retaliation for the United States sanctioning the police chief and other government officials last week.

"It would be too much a task for police to execute such an operation in two days time," he said, adding that investigations had begun a year ago.

The raid lasted about six hours.

Hong Kong Journalists Association chairman Chris Yeung said the massive police search operation at a media company is "shocking and terrifying."

"I have never seen it, maybe in some third world countries where the authorities have no respect for news freedom, but not Hong Kong," Yeung told reporters. "Governments that respect the fourth estate will not arbitrarily enter a media newsroom. The Hong Kong government is seriously violating press freedom."

The Committee to Protect Journalists is also urging that Lai be released and charges against him be dropped.

Hong Kong pro-democracy activist Agnes Chow speaks after being convicted at West Kowloon Court on Aug. 5, 2020, of rallying in an unauthorized protest that saw thousands of protesters besieging the police headquarters amid a rising anti-government movement in 2019. (Kyodo)

"The arrest of media tycoon Jimmy Lai bears out the worst fears that Hong Kong's National Security Law would be used to suppress critical pro-democracy opinion and restrict press freedom," Steven Butler, Asia program coordinator for the Committee to Protect Journalists, said in a statement.

The 22 pro-democracy camp lawmakers in a joint statement condemned police for the arrests and the raid at the media office, calling it a "disproportionately violent act that tramples on press freedom in the name of national security."

China's Foreign Ministry spokesman Zhao Lijian said in Beijing in response to Lai's arrest that Hong Kong is a society with rule of law, and China supports Hong Kong taking action according to the national security law.

Hong Kong's last colonial-era Gov. Chris Patten said the arrests and the raid were a major attack on Hong Kong's freedom.

"This is the most outrageous assault yet on what is left of Hong Kong's free press," concern group Hong Kong Watch quoted Patten as saying. "The arrests will be regarded by a growing number of people as another large step towards turning Hong Kong into a replica of Beijing's police state."

U.S. Secretary of State Mike Pompeo said that he is "deeply troubled" by the reports of Lai's arrest under Hong Kong's "draconian" national security law.

"Further proof that the CCP has eviscerated Hong Kong's freedoms and eroded the rights of its people," he tweeted, referring to the Chinese Communist Party by its acronym.

Peter Stano, the European Union's foreign affairs spokesman, said the arrests and raid of the daily's office "further stoke fears that the national security law is being used to stifle freedom of expression and of the media in Hong Kong."

Lai, along with 14 other democracy activists, had already been indicted for the organizing and incitement of people to join several unauthorized protests last year.

Four student activists were arrested last month for alleged secession and incitement for setting up, and encouraging others to join, a foreign organization advocating for Hong Kong independence.

Six other activists, who are outside Hong Kong, were also placed on a wanted list for inciting secession and collusion with foreign forces, the first time police have invoked the extraterritorial provision under the security law.

The maximum penalty for breaking the law is life imprisonment.