Hong Kong's government Wednesday announced a roadmap for leadership elections that offered no concessions to the city's democracy camp -- prompting a backlash from opposition lawmakers and warnings of more street protests.

Deputy leader Carrie Lam said the first-ever public vote for the post of chief executive in 2017 would be held in "strict compliance" with a ruling by China's National People's Congress last August.

That ruling stated that candidates for chief executive must first be approved by a loyalist committee, a decision that sparked more than two months of mass rallies which paralysed the city towards the end of last year.

Activists branded Beijing's framework -- universal suffrage based on pre-selected candidates -- as "fake democracy".

Analysts warned that protesters would likely mobilise once more if the bill is passed in the coming months.

Student leaders have already mooted the idea of an "Occupy Legco" movement to take over the legislature if the bill goes through.

"We are totally disappointed with the political reform package," said Joshua Wong, the teenage face of the protest movement.

He added that it was the "responsibility of the young generation" to oppose elections which stuck to Beijing's restrictions.

The small number of tents which remained on a road next to the government headquarters at the end of last year's protests has swelled to at least 140 in recent weeks.

Lam said that voters in 2017 would choose from two to three candidates selected by a 1,200-strong nominating committee.

That committee would reflect the current make-up of the pro-Beijing election committee, which up until now has chosen the city's leader, she said.

"These proposals are in strict compliance with the Basic Law (Hong Kong's constitution) and the relevant decisions of (China's) Standing Committee of the National People's Congress," Lam said.

"At the same time they fully take into account the views expressed by various sectors of the community," she added.

"It is neither practicable nor realistic to expect that one package of proposals can meet the ideals cherished by different people," she said.

Lam urged lawmakers to cooperate on passing the bill but most pro-democracy legislators marched out of the chamber following her speech.

"The pan-democrats would like to condemn strongly the government," said Civic Party lawmaker Alan Leong, one of those who walked out.

"We will launch a campaign to oppose the proposal and we will ask the Hong Kong public to continue to seek true universal suffrage," he added.

- Threat of protest -

"(The package) is very draconian, very harsh, very austere and shows no room for compromise," political analyst Willy Lam told AFP, saying that it was an extension of the hard line of China's President Xi Jinping.

"This reflects Xi Jinping's much more conservative line, not just on Hong Kong but in Taiwan and Tibet," Lam said.

He expressed surprise at the lack of movement on the composition of the nominating committee, which commentators had suggested could be made more representative of the general public.

Candidates can enter the first round of the leadership race with the backing of 120 members of the nominating committee. But they then need 50 percent support from the committee to move forward to the public vote.

Carrie Lam defended the voting procedure later Wednesday, saying that it offered pro-democracy candidates a higher chance of being nominated.

But Willy Lam said it would mean "no democratic candidate" would reach the public vote.

"If the government succeeds in passing the bill then it's quite possible there may be a few thousand protesters surrounding the legislative council building," he added.

Another political analyst Sonny Lo also warned of the "realistic possibility of confrontation".

"If the bill is passed, the 'Occupy Legco' movement would likely persist for some time," he said.

Hundreds of angry pro-government and pro-democracy protesters faced off outside the government complex Wednesday with minor scuffles -- dozens of police were patrolling the area.

A police spokeswoman refused to comment on whether extra security measures were being taken following the announcement.

The legislature said they would step up security at government headquarters from May 1, after protesters smashed windows there twice last year and stormed the building.

Measures include extra security checks, roller shutters and metal barricades.