Hong Kong Wednesday announced new proposals for how the city should choose its next leader but made clear that candidates would still be screened -- the key issue behind more than two months of mass protests.

More than 20 lawmakers carrying yellow umbrellas -- the symbol of the pro-democracy movement -- walked out of the legislative chamber as the consultation document was about to be presented by government number two Carrie Lam.

They shouted "I want universal suffrage" as they left the chamber, forcing a brief adjournment.

The document -- posted online so that residents can give their views -- outlines options for how leadership candidates will be nominated and for the composition of the nominating committee, which democracy campaigners fear will be stacked with pro-Beijing figures.

But Lam emphasised that the process would have to adhere to China's ruling that candidates must be vetted.

"Any attempt to revoke the Beijing decision is unrealistic," she said.

China has pledged that voters in Hong Kong can elect the city's next chief executive in 2017 -- the first time there has ever been a public vote.

But it insists that only two or three candidates can stand and that they will be vetted by a loyalist committee.

That decision sparked demonstrations that brought tens of thousands onto the streets at their height, before protest camps were cleared in December.

- 'Fake democracy' -

The government has billed the reform process as "historic" and says that it wants to reflect the pluralistic nature of Hong Kong society in the vote for the next leader. But campaigners have branded it fake democracy.

"We call on the Hong Kong government not to waste time but relaunch the political reform process," Alan Leong of the pro-democracy Civic Party said after walking out of the legislature Wednesday.

Leong had earlier been called a "running dog" -- a Chinese saying meaning traitor -- by pro-government protesters gathered outside the legislature waving a large Chinese flag.

Cyd Ho of the Labour Party added: "We cannot accept a vote after vetting because it doesn't offer real choices."

The consultation said one option was that anyone with 100 votes from the 1,200-strong nominating committee could start lobbying to become an official candidate for leader.

But the same committee would carry out a second round of vetting, with each final candidate needing to secure 50 percent support before standing for the public vote -- a stipulation of the Beijing ruling.

The consultation is the last official gauge of public opinion before a finalised proposal on electoral reform is put before the legislative council.

Pro-democracy lawmakers have vowed to vote against the plan unless it revokes the vetting of candidates.

If the final framework fails to pass with a two thirds majority it would mean a delay in the introduction of a public vote to Hong Kong.

"If the bill is not passed, Hong Kong's democratic development will be delayed... until 2022," Lam said.

"I urge democrats not to boycott the consultation or veto the bill."

But even senior member of the reform task force Raymond Tam said he was "pessimistic" it would go through.

Currently the city's leader is chosen by a pro-Beijing election committee.

Political analyst Sonny Lo said it was "too early to say" whether the final reform bill would be passed, as some pro-democrats could be persuaded by public opinion to vote for it.

"Public sentiment in Hong Kong is politically pragmatic. Most people would like to see a more harmonious way of discussion," he said.

There is still discontent and concern about China's increasing influence over the semi-autonomous city.

But many residents also became frustrated with the fragmented democracy movement and protest camps which brought parts of the city to a standstill.

Hong Kong was handed from Britain back to China in 1997 and enjoys freedoms not seen on the mainland.