Hong Kong students plan to occupy roads surrounding the city's British consulate in anger at a lack of support from London for their pro-democracy movement, as authorities ramp up pressure on protesters to go home.

The new plan emerged as President Barack Obama said the United States had played no role in Hong Kong's mass demonstrations, despite Chinese accusations that foreign forces are involved.

The city's government has urged protesters to leave the main rally sites that have brought parts of Hong Kong to a standstill for more than six weeks, with police authorised Monday to back up bailiffs charged with clearing barricades.

Activists say they want to show their anger at Britain for not standing up to China over "breaches" of the agreement the two countries made before Hong Kong was handed back to China by Britain in 1997, designed to protect Hong Kong's social systems and way of life.

"We are angry at the way that the British government has for many years denied that China has actually breached the declaration by interfering with Hong Kong politics," Anna-Kate Choi, the coordinator for the Occupy British Consulate group told AFP.

"They have the responsibility to make sure that the joint declaration has been implemented properly and that democracy and the high degree of autonomy of Hong Kong has been protected," Choi said.

She said she hopes for a turnout of hundreds and "maybe even thousands".

The group is a new offshoot of the protest movement, Choi added, with around 10 organisers from all walks of life including a secondary school student.

Protesters in Hong Kong are demanding fully free leadership elections for the semi-autonomous city in 2017.

But Beijing has refused to back down on its insistence that candidates must be vetted by a loyalist committee.

Bailiffs are expected to start a clearout operation in the next few days, with thousands of officers put on standby over the weekend, according to local media.

But seemingly undaunted, activists have put up large posters around the protest areas announcing the consulate occupation on November 21 and a Facebook page for the event has more than 700 likes.

The British consulate said they had no comment.

- 'Law and order must be maintained' -

President Obama met Chinese President Xi Jinping for talks in Beijing Wednesday.

"I was unequivocal in saying that the US had no involvement in fostering the protests that took place in Hong Kong," Obama told reporters at a joint press conference.

Xi said that the Occupy Central movement is illegal and that Beijing "firmly supports" the Hong Kong authorities in their efforts to control the situation.

"Law and order must be maintained in any case, not only in Hong Kong but everywhere in the world," he said.

Hong Kong residents enjoy rights not seen on the mainland, including freedom of expression and assembly.

However there are signs some of those rights are being curtailed, including physical and cyber-attacks on Hong Kong-based journalists critical of Beijing.

Activists say a policy "white paper", published by China in June, backtracked on the joint declaration by warning the city not to overstep the boundaries of its autonomy.

Britain and China are signatories of the 1984 Sino-British Joint Declaration, an agreement that enshrines the "one country, two systems" principle and states that until 2047 "the current social and economic systems in Hong Kong will remain unchanged."

British Prime Minister David Cameron said he was "deeply concerned" about escalating protests in the former British colony after police used tear gas on protesters at the end of September.

But activists feel that Britain is turning a blind eye and that China is eroding Hong Kong's freedoms.

Posters for the British consulate occupation bear the slogan: "China breaches the joint declaration, UK government respond now" with the pro-democracy movement's umbrella symbol emblazoned with the British flag.

"People in Hong Kong are feeling worried as Beijing's influence is getting much worse. I think occupying the British consulate will give the British some pressure to really have to face the Hong Kong people," engineering student Brian Ho, 19, told AFP.

"The British should be more active because Hong Kong used to belong to them... they should have spoken up for us a long time ago," 21-year-old protester King Kwong added.