Key Hong Kong democracy activist Agnes Chow and pro-democracy media boss Jimmy Lai have been released following their arrests a day earlier for alleged breaches of the security law, local media reported.

Chow, a former student group leader, and Lai were among several people who were arrested Monday on charges under a sweeping national security law.

Chow was released late Tuesday night, followed by Lai's release shortly after midnight.

Hong Kong democracy activist Agnes Chow speaks to media after being released on bail from the Tai Po police station on August 11, 2020 in Hong Kong, China. (Getty/Kyodo)

Speaking to reporters outside of a police station, Chow said that she had been arrested four times while engaging in social activities in Hong Kong but that the latest arrest was the scariest, according to local media.

"It's obviously a political prosecution and political suppression," Chow told reporters after she was freed on a HK$200,000 ($25,800) surety and cash bail. "The reason for arrest I was told was that I colluded with foreign forces by using social media between July and present, but the accusations were vague and I don't completely understand why I was arrested."

Chow said that her passport had been confiscated, adding that she is unsure whether she will be indicted.

Following his release, Lai and his lawyers were greeted by dozens of reporters and supporters of the newspaper outside the Mong Kok police station. He did not give comments before plowing his way through to his vehicle and leaving for home.

The Apple Daily, founded by Lai, said his two sons and four senior executives of the newspaper were all released on bail earlier. Lai was released on a HK$500,000 cash and surety bail.

Photo taken in Hong Kong on July 13, 2020, shows Hong Kong media mogul Jimmy Lai. Lai, one of the most famous democracy activists and critics of the Chinese Communist Party in Hong Kong, and six others were arrested on Aug. 10 for alleged collusion with foreign forces under a sweeping national security law recently imposed by China. (Kyodo)

Earlier Tuesday, China voiced dismay over Western governments' open support for Hong Kong's pro-democracy media boss and activists who were arrested on charges under a sweeping national security law.

Britain, Canada, the European Union and the United States have all expressed concerns and criticized the Hong Kong authorities for arresting Lai, his sons and colleagues using the anti-secession law newly imposed by China in the territory in late June.

Calling those criticisms "wrong remarks," China's ambassador in London Liu Xiaoming said Hong Kong's judicial matters are part of China's internal affairs, which should not be subjected to outside interference, and that the arrests were legal.

"Jimmy Lai and a small group of anti-China elements seeking to disrupt Hong Kong have colluded with external forces in acts and activities that jeopardize China's national security and challenge the limits of the law," Liu said, adding that rights and freedoms protected under the law have boundaries. "Anyone who crosses the boundaries and limits of the law shall be brought to justice."

Hong Kong police on Monday arrested Lai, founder of the liberal Apple Daily, his two sons and senior staff of the daily for alleged collusion with foreign forces and fraud while deploying some 200 police officers to search the media's head office for evidence.

Three other activists, including Chow and Wilson Li, a freelance journalist for Britain's ITV News, were also arrested for alleged breaches of the security law.

"This is further evidence that the national security law is being used as a pretext to silence opposition," British Prime Minister Boris Johnson's spokesman said. "Freedom of the press is explicitly guaranteed in the Sino-British Joint Declaration, and basic law, and is supposed to be protected under Article Four of the National Security Law."

Canadian Foreign Minister Francois-Philippe Champagne tweeted that Canada is "deeply troubled by the arrest of @JimmyLaiApple & others under China's National Security Law in Hong Kong. All human rights & fundamental freedoms, including media freedom & freedom of speech, must be upheld."

In the United States, the Congressional-Executive Commission on China in a joint statement urged the U.S. government to continue strongly opposing China's dismantling of Hong Kong's autonomy by means of its "vague" security law, used so as to justify human rights abuse and silence critics.

"The arrests of Jimmy Lai Chee-ying, Agnes Chow Ting, and other pro-democracy activists, along with the raid of Apple Daily Hong Kong are serious violations of human rights," the statement reads. "U.S. allies and partners should follow with their own sanctions and condemnations. The United Nations must follow suit and act as well."

U.S. Vice President Mike Pence also tweeted "The arrest of @JimmyLaiApple in Hong Kong is deeply offensive & an affront to freedom loving people around the world. The United States will continue to stand with Jimmy Lai and all the freedom loving people of Hong Kong. #FreeJimmyLai."

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

"The EU side openly interferes in Hong Kong affairs and China's internal affairs by making irresponsible remarks," a spokesman of the Chinese Mission to the European Union said. "China is firmly opposed to this."

"The constitutions of more than 100 countries in the world stipulate that the exercise of fundamental rights and freedoms must not endanger national security. The European Convention on Human Rights has similar provisions. The EU side should respect facts, reject double standards, and refrain from covering up or supporting criminal suspects," he said.

Copies of the newspaper were snatched up from newsstands throughout the day as people showed support for the daily, which said it increased printing from its normal average of 70,000 copies to some 550,000 copies to meet the present demand.

Investors also snapped up shares of Hong Kong-listed Next Digital, the holding company of Apple Daily, boosting its price by 330 percent with a turnover of HK$4.26 billion, making it the third-most traded stock on the Hong Kong bourse.