“[We must] establish a sound legal system and enforcement mechanism for safeguarding national security in the special administrative regions,” it said, without elaborating.

Macau introduced its own national security law 10 years ago but proposals for similar legislation in Hong Kong met stiff resistance.

The plenum sessions – attended by more than 300 full and alternate members of the Central Committee – provide an opportunity for the party’s most senior members to discuss and forge consensus on key policy issues. The reference to Hong Kong in the communique was evidence the city had featured on the agenda.

The reference to one country, two systems being an important part of China’s political system suggests Beijing has no plan to alter the arrangement but experts said the emphasis on the national security law suggested the leadership might push for local legislation in Hong Kong.

“With Article 23 not enacted for so long, there’s no law [in Hong Kong] that has proved to be effective in preserving national security in the city,” said Lau Siu-kai, vice-chairman of Beijing’s top think tank on Hong Kong affairs.

“Beijing doesn’t have much trust in the SAR government that it can complete the legislation, so it is likely to take active steps to address the issue and there are several ways to do it,” he said.

Lau said the National People’s Congress, China’s legislature, could issue an interpretation of the Basic Law, or enact a national law directed at Hong Kong.

It passed a similar bill in 2005 – the Anti-Secession Law – to target the pro-independence movement in Taiwan.

Beijing might also issue a mandate to Hong Kong’s Chief Executive Carrie Lam Cheng Yuet-ngor, Lau said.

Li Xiaobing, an associate law professor at Nankai University in Tianjin, said Macau was a good example of the concept of having a “legal system and enforcement mechanism for safeguarding national security”.

“Beside’s Macau’s national security law, which took effect in 2009 and is the legal system, in 2018 it also established a high-level committee to protect national security, chaired by its chief executive,” he said.

“That committee is the enforcement mechanism. Macau also banned non-Chinese judges from ruling on cases of national security.”

Hong Kong-based China watcher Johnny Lau Yui-siu said he expected to see a clear shift in policy direction as Beijing looks to strengthen its control over Hong Kong.

“This is clearly suggesting a wide range of unprecedented controls that are going to be exerted over Hong Kong as Beijing has lost its patience for one country, two systems,” he said.

“The communique sends a strong political message that might see Hong Kong respond by introducing new legislation to restrict free speech online, outlaw abuse of the police and increase controls on campus,” he said.

Alfred Wu, an associate professor at the Lee Kuan Yew School of Public Policy at the National University of Singapore, said the reference to national security underscored the party leaders’ determination to tighten their grip on Hong Kong despite the pressure coming from the United States.

“Although pushing for it might affect Hong Kong’s [free port] status, Beijing is determined to deal with the current turmoil firmly,” he said.

“From Beijing’s point of view, this might affect the ongoing trade talks [with the US] but it still believes that’s a better option than allowing Hong Kong to become a base of subversion.”

Additional reporting by Mimi Lau