Hong Kongers used the straw poll to express their desire for greater say in choosing their leader.
The vote is part of a campaign by activists in the southern Chinese city to ratchet up the pressure on authorities for democratic reform that could ultimately lead to a mass protest paralyzing the city's financial district.
Hong Kong, a freewheeling capitalist enclave of 7.2 million, passed from British to Chinese control in 1997 with the promise that it could retain a high degree of control over its own affairs under the principle of "one country, two systems."
Rising public discontent over mainland China's increasing influence has fuelled yearning for full democracy in Hong Kong, where residents can only vote for 40 of 70 lawmakers as well as local councilors.
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In what was seen as a thinly veiled threat ahead of the 10-day poll, Beijing released a policy document that said, among other things, that Hong Kong's autonomy comes at the discretion of the central government. The paper sparked a backlash, with more than 800 lawyers protesting Friday over a requirement for judges to be patriotic to China.
About 790,000 ballots had been cast by this evening, mostly online or through a smartphone app, although 62,000 were cast at polling stations.
Voters had a choice of three proposals on democratic reform, all of which included so-called public nomination. Occupy Central organisers have vowed to rally 10,000 people in a mass protest aimed at crippling the central business district if the government fails to come up with reform proposals that don't meet international standards.