By Emily Chung and Adam Rose
HONG KONG (Reuters) - More than 780,000 votes were cast by Sunday, the final day of an unofficial referendum on democratic reforms in Hong Kong, part of a civil campaign that has been branded illegal by local and mainland Chinese authorities.
Hong Kong, a free-wheeling, capitalist hub of more than seven million people, returned to Chinese rule in 1997 with wide-ranging autonomy under a "one country, two systems" formula, along with an undated promise of universal suffrage.
While Beijing says Hong Kong can go ahead with a vote in 2017 for the city's top leader, Hong Kong's mini-constitution, the Basic Law, specifies that only a nominating committee can pick leadership candidates.
Democracy activists want the nomination process to be open to everyone, in line with international standards, and have threatened to lock down the Central area of Hong Kong, home to some of Asia's biggest companies and banks, if the city fails to adopt a strong democratic method for electing its next leader.
"I think the signal has already been sent to Beijing that Hong Kong people are prepared to express their views on universal suffrage," said Benny Tai, associate professor of law at the University of Hong Kong and one of the organizers of the vote and the movement, Occupy Central with Love and Peace.
"We hope the result of the civil referendum will be taken seriously by the SAR (Special Administrative Region of Hong Kong) and Chinese government."
The unofficial vote, organized by pro-democracy activists, has been conducted mainly online. Voters are required to give their identification number to prevent cheating.
At a "polling booth" at Chinese University of Hong Kong on Sunday, a small group of pro-Beijing supporters with mainland accents held up banners denouncing the vote, while four people jumped into the city's Victoria Harbour to protest against the referendum and were quickly rescued.
Another pro-Beijing group, Caring Hong Kong Power, marched through the busy shopping district of Causeway Bay carrying bright orange balloons and urging people not to vote.
Group spokeswoman Lee Ka-ka handed a petition to police signed by 30,000 against the Occupy Central group. She also urged police to "act strongly against the movement".
Results of the online referendum are expected to be released at around 11 p.m. local time on Sunday, with the overall tally set to be announced on Monday. Residents have voted on the Internet, and at polling booths.
The last day of voting coincided with China's military opening its barracks in Hong Kong to the public, giving curious tourists a rare glimpse inside two outposts, as tensions between local democracy activists and Beijing continues to heat up.
The referendum wraps up just two days ahead of an annual demonstration on July 1, the anniversary of Hong Kong's return to Chinese rule, a date citizens use to protest against multiple issues, including what they perceive as foot-dragging on democratic reforms.
Tai urged those who had voted to turn up on July 1 to demonstrate their commitment to universal suffrage.
WHITE PAPER "BACKFIRED"
The 10-day poll, organized by Occupy Central, comes at a time when many Hong Kong residents fear civil liberties are being eroded and amid growing concern about the rule of law in the Asian financial center.
On Friday, Hong Kong lawyers dressed in black marched through the city to protest against the wording in a white paper released this month by Beijing in which it said being patriotic and "loving the country" is a basic requirement for the city's administrators, including lawyers. [ID:nL4N0P81NB]
The lawyers were taunted by pro-Beijing groups shouting into loud hailers as they marched to the Court of Final Appeal.
Many recent rallies in Hong Kong have seen scuffles break out between pro and anti-Beijing groups, including the 25th anniversary of the June 4, 1989, crackdown on pro-democracy protests in and around Beijing's Tiananmen Square, an event that had always been peaceful in Hong Kong.
Tai said on Sunday the white paper, which reasserted Beijing's control over the former British colony, had "backfired" and prompted more people to vote.
Pro-Beijing newspapers, Chinese officials and Hong Kong business tycoons have strongly criticized the Occupy Central campaign, saying it could hurt the city's standing as a financial center.
The big four audit firms were the latest to join the chorus, when they took out adverts in local Hong Kong newspapers on Friday warning that investors could leave the city if mass protests go ahead. [ID:nL4N0P827B]
Activists say it is a peaceful movement demanding a "genuine choice" for Hong Kong's voters.
The unofficial referendum is seen as an important test for pro-democracy activists who believe the public are dissatisfied with the pace of political reform promised by Beijing.
(Additional reporting by Grace Li, Adam Rose, Nikki Sun and James Zhang; Writing by Anne Marie Roantree; Editing by Jeremy Laurence and Sophie Hares)