Hong Kong's chief hit back at "uncivilised" critics on Thursday after he was booed and heckled by local residents as he tried to promote a newly unveiled, Beijing-backed plan for leadership elections in 2017.

The roadmap for the city's first ever public vote for its chief executive was announced on Wednesday. It conforms to a controversial ruling from Beijing stipulating that candidates must be pre-screened by a loyalist committee.

That ruling sparked mass protests which lasted more than two months towards the end of last year.

The government kicked off a promotional campaign to sell the plan after its launch but Chief Executive Leung Chun-ying and his deputy, Carrie Lam, were drowned out by protesters as they visited a middle-class district late Wednesday.

"Yesterday during the district visit... there were some hecklers who kept using loud voices and quite uncivilised words to try to speak over others," Leung told reporters Thursday.

"It's not democratic behaviour," he said. "We don't want to see such scenes at every district visit."

Protesters booed Leung and Lam and blocked their path with yellow umbrellas, a symbol of the democracy movement.

The election proposal triggered a backlash from pro-democracy lawmakers and student leaders, and was slammed by Human Rights Watch, which described it as a "betrayal".

Britain handed Hong Kong over to China in 1997 under a joint declaration which guaranteed political, social and economic freedoms not enjoyed on the Chinese mainland.

The semi-autonomous city is governed under that "one country, two systems" deal, but there are fears that freedoms are being eroded by increased influence from Beijing.

- Government 'betrayal' -

Currently the city's leader is chosen by a 1,200-strong election committee.

Beijing has promised universal suffrage for the 2017 vote, but has said that candidates must be approved first by a nominating committee.

The constitutional reform package is "legal, feasible, rational and practical", China's Hong Kong and Macau Affairs Office said on Wednesday, according to state news agency Xinhua.

"The central government consistently supports efforts to advance the democratic development" in Hong Kong, it added.

But pro-democracy lawmakers have vowed to block the roadmap when it goes to a vote in Hong Kong's legislature in the coming months.

Civic Party legislator Kwok Ka-ki called the government "irresponsible" and said that the reform package "in no way" gave the Hong Kong people a real choice.

"We will be very cautious in making sure the people can get the real message instead of receiving a lot of fake messages and lies told by the government," he told AFP, saying that the opposition campaign would launch Sunday.

Sophie Richardson, China director for Human Rights Watch, described the election plan as an "utter capitulation to Beijing" and a "betrayal of democratic aspirations in Hong Kong".

"The right to vote and the right to stand for election are fundamental human rights," she said.

"That the Hong Kong authorities are denying half that equation is a rejection of international law and of the promise of democracy for the citizens there."

Human Rights Watch said the screening of candidates would violate the International Covenant on Civil and Political Rights.

But justice secretary Rimsky Yuen accused the city's democracy camp of depriving Hong Kong citizens of a chance to vote by trying to block the bill Thursday.

"It's not they who are the only sector in the Hong Kong community that we need to take into account," he said.