A total of 792,808 voters took part in an unofficial referendum on universal suffrage in Hong Kong, organisers said.
The 10-day poll was held by protest group Occupy Central.
Campaigners want the public to be able to elect Hong Kong's leader, the chief executive. The Hong Kong government says the vote has no legal standing.
About 42% of voters backed a proposal allowing the public, a nominating committee, and political parties to name candidates for the top job.
Beijing has pledged that the Hong Kong public can directly choose its chief executive in the 2017 election, but only from a list of candidates selected by a nominating committee.
Activists fear China will use the committee to screen out candidates it disapproves of.
Occupy Central organised the vote for the public to decide which of three proposals - all of which involve allowing citizens to directly nominate candidates - to present to the Beijing government.
The winning proposal, put forth by the Alliance for True Democracy, allows candidates to be nominated by 35,000 registered voters, or by any political party which secured at least 5% of the vote in the last election for Hong Kong's legislative committee.
The proposal also allows a nominating committee to name candidates, and the formation of this committee should be "as democratic as it can be", reported the South China Morning Post.
The other two proposals in the referendum allowed only the public and a nominating committee to name candidates.
The voting, in polling stations or on the popvote.hk website, began on 20 June. The deadline was originally set for 22 June, but was later extended after what organisers claimed were several cyber attacks on the website.
Popvote.hk was designed by the University of Hong Kong and Hong Kong Polytechnic University to measure support for Occupy Central's campaign.
Chan Kin-man, sociology professor at the University of Hong Kong and one of the founders of Occupy Central, praised the turnout and declared the referendum a success.
"It is very unexpected. It is a very encouraging sign," he said.
"I believe that people feel that our autonomy has been threatened and is going to be threatened even more by Beijing. People feel outrageous [sic outraged] and so they want to make their voice heard."
The BBC's Juliana Liu in Hong Kong says the large turnout - about one in five registered voters - sends a strong message that a significant part of the Hong Kong public is unhappy with the Chinese government's plans for reform.
Pro-Beijing groups have opposed the referendum, with one group marching through the Causeway Bay district with orange balloons urging people not to vote and handing a petition with 30,000 signatures to police.
The vote is seen as a prelude to a campaign of dissent that could shut down Hong Kong's financial district, our correspondent adds.
Prof Chan said the protests could turn violent.
"We have been witnessing more and more physical confrontation during protests and I believe that more young people are willing to go to jail or even to confront the police and the government with their own bodies," he said.
"As a professor, as a parent we want to protect our young generation, that's why we believe we are now in a very critical juncture of our history."
Hong Kong was handed back to China in 1997 following a 1984 agreement between China and Britain.
China agreed to govern Hong Kong under the principle of "one country, two systems", where the city would enjoy "a high degree of autonomy, except in foreign and defence affairs" for 50 years.
As a result, Hong Kong has its own legal system, and rights including freedom of assembly and free speech are protected.