Hong Kong national security police conducted a fresh raid on pro-democracy newspaper Apple Daily on Thursday, arresting five executives and carting off computers in the latest blow to the outspoken tabloid.

The paper and its jailed owner Jimmy Lai have long been a thorn in Beijing's side with unapologetic support for the financial hub's pro-democracy movement and scathing criticism of China's authoritarian leaders.

Apple Daily editor-in-chief Ryan Law in the paper's newsroom in Hong Kong last month Apple Daily editor-in-chief Ryan Law in the paper's newsroom in Hong Kong last month Photo: AFP / ISAAC LAWRENCE

More than 500 officers conducted a dawn operation which authorities said was sparked by articles Apple Daily had published "appealing for sanctions" against Hong Kong and China's leaders.

It is the first time the content of media reporting has sparked arrests under the national security law.

In a message to readers, Apple Daily warned Hong Kong's press freedoms were "hanging by a thread", but vowed to "stand tall".

A shadow of fear hangs over Hong Kong's outspoken and staunchly pro-democracy Apple Daily newspaper, with its billionaire owner Jimmy Lai now jailed and many reporters asking themselves: "Are we next? A shadow of fear hangs over Hong Kong's outspoken and staunchly pro-democracy Apple Daily newspaper, with its billionaire owner Jimmy Lai now jailed and many reporters asking themselves: "Are we next?" Photo: AFP / Peter PARKS

Its union described the operation as a "wanton violation of press freedom" that "displayed how much police power has inflated under the national security law".

The United States condemned the raid as "entirely politically motivated" and aimed at silencing dissent in Hong Kong, long a hub for international finance and media.

"We call on authorities to stop targeting the independent and free media," State Department spokesman Ned Price told reporters.

Police have raided the Apple Daily newsroom for a second time in the latest hammer blow to the outspoken tabloid Police have raided the Apple Daily newsroom for a second time in the latest hammer blow to the outspoken tabloid Photo: AFP / Peter PARKS

"Efforts to stifle media freedom and to restrict the free flow of information not only undermine Hong Kong's democratic institutions but they also hurt Hong Kong's credibility and viability as an international hub."

British Foreign Secretary Dominic Raab said China was using security legislation in Hong Kong to "target dissenting voices, not tackle public security".

"Freedom of the press is one of the rights China promised to protect in the Joint Declaration & should be respected," he said, referring to the deal under which the city was returned to Chinese rule in 1997.

Hong Kong police have arrested Apple Daily's editor-in-chief Ryan Law "for collusion with a foreign country or with external elements to endanger national security Hong Kong police have arrested Apple Daily's editor-in-chief Ryan Law "for collusion with a foreign country or with external elements to endanger national security" Photo: AFP / ISAAC LAWRENCE

Hong Kong police said the five Apple Daily executives were arrested for collusion with a foreign country or external elements "to endanger national security".

Authorities also seized HK$18 million (US$2.3 million) in Apple Daily assets, the first time a national security law seizure order has been made directly against a Hong Kong media company, rather than an individual.

Beijing has made no secret of its desire to see the pro-democracy voice of Apple Daily tamed Beijing has made no secret of its desire to see the pro-democracy voice of Apple Daily tamed Photo: AFP / Peter PARKS

Hong Kong has long been a major international media hub but its press freedom ranking has slipped dramatically in recent years.

Police officers leave the Apple Daily newspaper offices in Hong Kong Police officers leave the Apple Daily newspaper offices in Hong Kong Photo: AFP / Anthony WALLACE

Secretary for Security John Lee declined to say which articles breached the security law or whether those who shared the articles online, or bought Apple Daily or its shares might be at risk.

"Our actions are not targeting press freedom or journalistic work," he added. "We target perpetrators who would use journalistic work as a tool to engage in acts that endanger national security."

Sharron Fast, a lecturer at the University of Hong Kong's journalism school, described Lee's comments as "ominous and incorrect".

Cheung Kim Hung, CEO and Executive Director of Next Digital Ltd, is escorted by police into the Apple Daily newspaper offices in Hong Kong Cheung Kim Hung, CEO and Executive Director of Next Digital Ltd, is escorted by police into the Apple Daily newspaper offices in Hong Kong Photo: AFP / Anthony WALLACE

"It is precisely the role of a journalist in a free society to report on political views, even those that might be unwelcome," she told AFP.

Among the arrested executives were chief editor Ryan Law and CEO Cheung Kim-hung.

Hong Kong's stock exchange said trading in shares of Next Digital -- the publisher of the newspaper -- had been halted.

After the raid, reporters returned to a semi-gutted newsroom, with the paper saying 38 computers were taken away as well as hard drives and reporters' notepads.

A photographer, who gave just a nickname KT, said the latest operation had "created terror for every Apple Daily worker".

"If I get arrested for reporting the news, I will have no regrets," he told AFP.

Executive chief editor Lam Man-chung, who was not among those arrested, told AFP that staff would "try all our best to publish newspapers for tomorrow".

The security law is the speartip of a sweeping crackdown on Beijing's critics in Hong Kong since 2019's huge democracy protests.

It has criminalised much dissent, given China jurisdiction over some cases and awarded authorities a suite of powerful new investigation powers.

Those convicted face up to life in prison, and most are denied bail after arrest.

Thursday's raid was the second on Apple Daily in less than a year.

The tabloid's billionaire owner Lai, 73, was charged with collusion after hundreds of officers searched the paper's newsroom last August.

He is currently serving multiple jail sentences for attending various protests.

Beijing has made no secret of its desire to tame the paper, with state media routinely describing Lai as a "traitor" and a "black hand".

Last month, police used the national security law to freeze Lai's bank accounts and his majority shares in Next Digital.

Until Thursday's raid, authorities had left the company's assets alone. It is unclear whether Apple Daily will now be able to pay its staff.

More than 100 people have been arrested under the law, many of them among the city's best-known democracy activists. Other campaigners have fled overseas.