Hong Kong police used a sweeping national security law Thursday to arrest five editors and executives of a pro-democracy newspaper on charges of colluding with foreign powers — the first time the legislation has been used against the press in yet another sign of an intensifying crackdown by Chinese authorities in the city long known for its freedoms.

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.

The newspaper said in a statement that the move left it “speechless” but vowed to continue its reporting and even invited other media outlets to watch the Friday editions roll off the presses, a show of its commitment to continue its work.

Apple Daily has long been one of the most outspoken defenders of Hong Kong’s freedoms and in recent years has often criticized the Chinese and Hong Kong governments for walking back promises that the territory could retain those freedoms for 50 years after the former British colony was handed over to China in 1997.

The newspaper has thus found itself a frequent target. Apple Daily founder Jimmy Lai is currently serving a 20-month prison sentence after being convicted of playing a role in unauthorized protests in 2019, when Hongkongers took the streets in massive antigovernment demonstrations in response to a proposed extradition law that would have allowed suspects to stand trial in China. Protests grew to include calls for broader democratic freedoms, but the movement only appeared to harden Beijing’s resolve to limit civil liberties in the territory, including by imposing the national security law used in Thursday’s arrests.

The legislation outlaws secession, subversion, terrorism and foreign collusion and has been used to arrest over 100 pro-democracy figures since it was first implemented a year ago, with many others fleeing abroad. The result is that it has virtually silenced opposition voices in the city — and drawn sanctions from the U.S. against Hong Kong and Chinese government officials.

Also read: Hong Kong democracy activist Agnes Chow released from jail

Those arrested Thursday included Apple Daily’s chief editor Ryan Law; the CEO of its publisher Next Digital, Cheung Kim-hung; the publisher’s chief operating officer; and two other top editors, according to the newspaper.

Police also froze 18 million Hong Kong dollars ($2.3 million) in assets belonging to three companies linked to Apple Daily, said Li Kwai-wah, a senior superintendent at Hong Kong’s National Security Department.

Trading in shares of Next Digital was halted Thursday morning at the request of the company, according to filings with the Hong Kong stock exchange.

In an apparent show of force, more than 200 police officers were involved in the search of Apple Daily’s offices, and the government said a warrant was obtained to look for evidence of a suspected violation of the national security law.

Apple Daily published a letter to its readers, saying that police had confiscated many items during the search, including 38 computers that contained “considerable” journalistic material.

“Today’s Hong Kong feels unfamiliar and leaves us speechless. It feels as though we are powerless to stop the regime from exercising its power as it pleases,” the letter read. “Nevertheless, the staff of Apple Daily is standing firm. We will continue to persist as Hongkongers and live up to the expectations so that we have no regrets to our readers and the times we are in.”

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.

He alleged that the police action against the Apple Daily editors and executives is not related to “normal journalistic work.”

“The action targeted the use of journalistic work as a tool to endanger national security,” he said.

In a chilling warning, he said that anyone working with the “perpetrators” would “pay a hefty price.” He added: “Distance yourself from them, otherwise all you will be left with are regrets.”

Also read: Hong Kong vigil organizer arrested on Tiananmen anniversary

The Chinese government’s liaison office in Hong Kong said in a statement Thursday that it supported police action, noting that while the city’s mini-constitution, the Basic Law, guarantees the freedoms of speech and press, those rights cannot undermine the “bottom line of national security.”

“Freedom of the press is not a ‘shield’ for illegal activities,” the liaison office said.

Experts said that, with the arrests, the government has sent a message that certain topics are off limits.

“This is a direct attack on Apple Daily, and on press freedom in Hong Kong,” said Thomas Kellogg, executive director of the Georgetown Center for Asian Law. “I fear that the arrests will send a message to media outlets across Hong Kong, that certain red lines will be enforced … and that those who cross them risk the possibility of arrest and of jail time under the national security law.”

Hong Kong Journalists Association Chairman Chris Yeung echoed those concerns, saying the national security law was being used as a “weapon to prosecute media executives and journalists.”

He said that the court warrant that allowed police to search the offices of Apple Daily had undermined journalists’ ability to protect their materials, a vital part of upholding press freedom.

“Self censorship will get worse if journalists are not sure whether they are able to protect their sources of information,” said Yeung.