In a statement on its verified Facebook page, the publication said it produced 550,000 copies on Tuesday — up from its normal circulation of about 70,000. In a post Monday, it urged people in Hong Kong to buy the paper and show their support, a message seemingly heeded by many people who were seen lining up for copies.

Shares of Next Digital, the newspaper's parent company, have skyrocketed more than 1,100% in Hong Kong this week, albeit to the equivalent of about 14 US cents — another sign of support among locals.

Lai was arrested Monday on suspicion of "colluding" with foreign forces, according to local police. The offense was created by a new national security law imposed on the city by Beijing last month.

Police said at least nine other people were also arrested in national security operations on Monday. Two of Lai's sons were among them. A livestream uploaded to Facebook by Apple Daily the same day showed police searching the company's newsroom.

On Tuesday, the paper's front page featured an image of Lai being arrested, and the headline: "Apple Daily must maintain its operations." It also included a statement, which said the newspaper condemned — and was "deeply angry" — about the police operations.

Next Digital also vowed to "fight on."

"Hong Kong's press freedom is now hanging by a thread," it said in a statement. "The staff of Apple Daily will stay fearless and continue speaking the truth amid persecution."

Police said in a statement Monday that officers of its newly created National Security Department had conducted the search operation after an "in-depth investigation," and with a warrant issued by a magistrate.

The people who were arrested were suspected of "collusion" with foreign forces to endanger national security, and "conspiracy to defraud," police said in a statement.

Authorities noted that the investigation was continuing, and that more arrests could be made.

A spokesperson for China's Hong Kong and Macao Affairs Office, which is run by the country's State Council, also spoke out on the issue Monday, saying that it "firmly supports" the arrests of Jimmy Lai and others who were apprehended.

"People who colluded with foreign forces to endanger national security should be sternly punished under the law," the representative said in a statement.

The arrest has raised concerns over the future of Hong Kong's media.

"A month or two ago, nobody could think that in Hong Kong, media organizations could be searched like this," Hong Kong Journalists Association chairperson Chris Yeung said Monday.

"We never thought that this could happen in Hong Kong," he added. "This is very sad."

The Foreign Correspondents' Club in Hong Kong (FCC) has also condemned Lai's arrest and the raid on Apple Daily, calling it "a direct assault on Hong Kong's press freedom."

The Office of the Commissioner of the Ministry of Foreign Affairs of China in Hong Kong criticized the FCC, accusing it of "smearing" the local police force.

The office accused the organization of trying to "whitewash and justify Jimmy Lai and other criminal suspects."

"Lawbreakers shall be held accountable, and no one shall be above the law," the office said Tuesday.