The Foreign Ministry said on Monday that Jimmy Lai's 20-year prison sentence was legitimate and reasonable, given his three convictions of colluding with foreign forces and publishing seditious materials.

Spokesman Lin Jian stressed the SAR is governed by the rule of law and that Beijing firmly supports Hong Kong in safeguarding national security and punishing crimes in accordance with the law.

"Jimmy Lai is a Chinese citizen. He is the main planner and participant in a series of anti-China and destabilising activities," he said during a regular press briefing.

"His behaviour seriously violated the principle and bottom line of One Country, Two Systems, seriously damaged national security, the prosperity and stability of Hong Kong and the people's well-being, and should be punished by law."

Lin also stressed that Hong Kong's judiciary is doing its duty to safeguard the authority of the law, adding that protecting national security is reasonable, legitimate and lawful.

The Hong Kong and Macao Affairs Office said Lai was the mastermind behind turning the controversy over extradition bills in 2019 into "Hong Kong's version of a colour revolution", causing serious damage such as some people calling for "Hong Kong independence".

"Now that Lai has finally been severely punished, it once again proves the traditional saying: justice may be delayed, but it shall never be denied," the office said in an article published on its official WeChat account platform.

It added that Lai's crimes would be considered serious offences anywhere in the world with national security a top priority.

His sentencing, the office said, sends a powerful message that whoever challenges security laws will be severely punished as it also fully reflects the unity of Hong Kong society in condemning the anti-China mastermind.

Beijing's Liaision Office in Hong Kong stressed that during Lai's trial, some politicians from countries like the United States and the United Kingdom had shown double standards by interfering in China's internal affairs and the Hong Kong judiciary.

"They had disregarded fundamental principles of international relations, flouting their own nation's stringent national security legislation, and ignoring the irrefutable evidence against Lai," it said in a statement.

"They have colluded with anti-China elements who fled overseas by openly supporting and shielding Lai and whitewashing his crimes, and exerted pressure through interference in a futile attempt to absolve him of his crimes."

Beijing's Office for Safeguarding National Security in Hong Kong said that every place in the world has the responsibility to severely punish criminal acts that endangered national security as well as safeguard security in accordance with the law.