Organisers of a pro-democracy group who vowed to take over Hong Kong's streets admitted Tuesday they were powerless to change China's plan to vet candidates for the city's next leader, but said their protest would go ahead.

The admission came after activist leaders promised a new "era of civil disobedience" in front of thousands of supporters at a Sunday rally after Beijing crushed hopes for full democracy.

"We have to admit the fact that up to this point it is quite unrealistic to think that our action will change the decision made by Beijing," Occupy Central co-founder Chan Kin-Man told AFP.

"The first function about talking about Occupy Central is to create pressure for compromise and negotiation. Now I believe we have already reached the end point in terms of the democratic change in the system," Chan said.

He also said the movement could end if the city's legislature vetoes the proposed electoral changes.

However Chan said direct action was still planned, mobilising thousands of people to block major thoroughfares in the financial district of Central to protect the city's "core values" and "existing rights and liberties".

But he acknowledged that supporters who are more "pragmatic" may back down.

"Ten thousand protesters was our target set in the past, we are still confident that thousands of people will join and it will last at least for days."

A statement from Occupy late Tuesday appeared, however, to backtrack on comments that support might wane.

"It is not correct to say we have less support," it read. "Although some pragmatic supporters may leave, new supporters are joining us because they are angry about the Chinese government's decision."

- Angry demonstrations -

Analysts said the movement may be changing tactics to dig in for a long-haul battle against Beijing.

"It is definitely a backing down but it is a strategic backing down," Surya Deva, a professor at City University of Hong Kong's School of Law told AFP.

"They know they can't really get the desired change by a short, intensive burst of civil disobedience. They're getting ready perhaps for a long term campaign -- and they need to build a base," he added.

Hong Kong police have arrested 22 people during a series of protests targeting a senior visiting Chinese official, authorities said Tuesday.

In the kind of scenes that would be unthinkable on the mainland, Li Fei, a senior member of China's rubber-stamp parliament, has been dogged by angry demonstrations throughout his visit to the former British colony -- including lawmakers heckling him during a speech on Monday.

Britain handed Hong Kong back to China in 1997 under an agreement which allows civil liberties not seen on the mainland, including free speech and the right to protest.

Li is visiting the semi-autonomous Chinese city to explain Beijing's controversial decision to control who can stand in the city's next leadership election in 2017.

Protesters have kept a vigil outside his hotel, with renewed scuffles breaking out late Monday.

Officers made 19 arrests outside the hotel that night -- 18 for "unlawful assembly" and one for obstructing a police officer.

- Pepper spray -

Earlier Monday police used pepper spray on demonstrators at a convention centre where Li gave a speech punctuated by regular interruptions by protesters and pro-democracy lawmakers.

Three people were subsequently arrested for disorder in a public place, police told AFP.

The standing committee of China's National People's Congress or parliament said Sunday Hong Kong citizens would be allowed to elect their next leader in 2017 -- but candidates must be chosen by a pro-Beijing committee and must win the backing of more than half of the committee members to stand.

Only two or three will be allowed to stand for election. Democracy activists say the rules mean China will be able to ensure that only pro-Beijing candidates can contest the vote.

The proposal must win two-thirds support in Hong Kong's 70-seat legislature to pass.

"When the proposal is vetoed by the legislative council and if there is no more hope for restarting the whole reform process, then our movement has to stop there," Chan said.

China on Tuesday accused London of interfering in its domestic affairs, over a British parliamentary inquiry into democratic reforms in Hong Kong.

The public rebuke followed reports Monday that Chinese authorities had written to the parliamentary foreign affairs select committee to demand the probe be dropped.

"Hong Kong has returned to the motherland," said China's foreign ministry spokesman Qin Gang.

"Issues concerning the political reform of Hong Kong fall totally within China's domestic affairs, which allows no interference from the outside."