Beijing's denial of open elections for Hong Kong's next leader demonstrates the ruling Communist Party's desire for complete political control and its resolve to quash any opposition, whatever the cost, observers say.

The standing committee of China's rubber-stamp parliament on Sunday ruled out public nominations for Hong Kong's next chief executive in 2017, with candidates for the city's top job to be approved instead by a Beijing-backed committee.

The move by the National People's Congress (NPC) drew fury and pledges of a mass sit-in by Hong Kong's pro-democracy campaigners, who say Beijing is working to weed out any potential critics of the Communist Party.

But the authorities dismiss such protestations, insisting that a popular vote between the chosen contenders fulfils their pledge of "universal suffrage".

Some experts say any expectations Beijing would loosen its grip in the former British colony -- where London appointed its leaders, and which returned to China in 1997 -- were unrealistic in the first place.

The decision came as Chinese President Xi Jinping rolls out a national crackdown on dissent since taking office last year, with authorities suppressing online debate and detaining activists.

"The mainland has its view, which will not be shaped by the Hong Kong people," said Shen Dingli, a professor at Shanghai's Fudan University.

Mainland authorities, he said, "want to have a person that will listen to Beijing". The pro-democracy activists, he added, "cannot persuade Beijing, because these people don't listen to Beijing".

China's political system is controlled by the Communist Party, and while it has long permitted elections at the village level, it typically keeps a tight grip on the process, with approved candidates often running unopposed. There are no direct polls at higher levels.

The State Council, China's cabinet, reasserted Beijing's control over Hong Kong in a policy "white paper" in June.

Jia Qingguo, associate dean of Peking University's School of International Studies, said the NPC decision was "absolutely necessary" to end debate in Hong Kong.

"If the NPC makes its decision very clear, this will help stabilise Hong Kong," he said. "The NPC is China's most powerful organ, so when it speaks, it speaks with authority."

- 'Crisis of governance' -

Residents of Hong Kong enjoy rights not seen on the mainland, including freedom of expression and assembly, as well as an independent legal system.

But there are signs some of those rights are beginning to be curtailed, especially media freedom, with physical and cyber-attacks on Hong Kong-based journalists critical of Beijing, and independent website House News shutting its doors last month.

Surya Deva, a professor at the City University of Hong Kong, said Beijing wants to "control the political governance in Hong Kong".

But the NPC's decision violated both the city's Basic Law and the 1997 joint declaration between the British and Chinese governments, he argued, and was "likely to prove counterproductive".

"Hong Kong is going to face a crisis of governance in the near future if the central government continues to behave in this way," he said.

- System 'cannot be trusted' -

The move is also likely to have repercussions in Taiwan, to which the defeated Nationalists fled at the end of China's civil war in 1949 and which Beijing considers a renegade province.

Beijing has a standing offer of reunification with Taipei along the lines of the "one country, two systems" model that applies in Hong Kong.

But Lai Chung-chiang, a lawyer and rights activist who played a major role in Taiwan's unprecedented student-led movement earlier this year, told AFP: "The example of Hong Kong has clearly told lots of people in Taiwan that the political mechanism of 'one country, two systems' does not work and cannot be trusted."

He Weifang, an outspoken law professor at Peking University, warned on his Sina Weibo microblog that "right now, before our eyes, we are obviously pushing Taiwan further away".

Nonetheless the Party's decision will ultimately prevail, experts say.

In Hong Kong, Occupy Central activists initially promised "wave after wave" of demonstrations, but the group's co-founder Chan Kin-man admitted to AFP on Tuesday that they were powerless to overturn Beijing's decision.

Ray Yuen, a 20-year-old student who waited outside a Hong Kong hotel to boo NPC official Li Fei, was adamant the campaigners would protest "until the end of time" -- but acknowledged that power rests in the Party's hands.

"I believe the Chinese government will not give us true democracy, but we're still here," he said. "We know what democracy means, we are not sheep."

Fudan University's Shen insisted there was no room for debate following Sunday's announcement.

"That's the end. No 'next'," he said. "Beijing announced the legal decision, so what can they do?

"If they protest, they will be sent to jail. This is a country ruled by law."