HONG KONG (AFP) - More than half a million people have voted in an unofficial Hong Kong electoral reform poll, organisers said on Saturday, in a ballot hit by a massive cyberattack and labelled by Beijing as "illegal".
Online polling started on Friday at noon and 500,436 residents had taken part in the "civil referendum" by 3.00pm local time on Saturday (0700 GMT).
The poll asks how voters would like to choose their next leader.
The former British colony's leader is currently appointed by a 1,200-strong pro-Beijing committee but there have been increasingly vocal calls for residents to be able to choose who can run for the chief executive post.
China has promised direct elections for the next chief executive in 2017, but has ruled out allowing voters to choose which candidates can stand.
Participation in the informal ballot has already beaten all expectations, surprising even its organisers, the Occupy Central movement. The pro-democracy group said before launching the exercise, which runs until June 29, that they were hoping for 300,000 people to take part.
The 500,000 who had voted in the first 27 hours of the poll represents a sizeable chunk of the 3.47 million people who registered to vote at elections in 2012.
The ballot allows registered permanent residents to vote through a website or on a smartphone app and there are plans to open polling booths around the city on Sunday. But the online voting system has been targeted by a massive denial-of-service attack, with organisers swift to point the finger at China.
"We have reasonable suspicion to believe that Beijing was behind the attacks because which authority would have the resources and motivation?" Mr Benny Tai, one of the founders of the Occupy Central movement, told AFP. "It's unprecedented in Hong Kong," Mr Tai said of the size of the attack.
Under the "one country, two systems" agreement reached when the city of seven million people was handed over from Britain to Communist-ruled China in 1997, Hong Kong has guaranteed civil liberties not enjoyed on the mainland, including free speech and the right to protest.
The poll allows residents to choose between three options for how they would like to see the 2017 chief executive ballot carried out - each of which would allow voters to choose candidates for the top job and therefore be considered unacceptable by Beijing.
Many pro-democracy activists fear that Beijing will handpick the candidates to ensure that the job does not go to anyone who would be critical of China.
China's State Council, the equivalent of its cabinet, said on Friday that any referendum on how Hong Kong elects its leader would not have constitutional grounds and would be illegal and invalid, state news agency Xinhua reported. The comments appeared to have little impact on voters.
"More and more people see that this is a very critical moment and they must voice their views, not just to have their say about democratic rights, maybe also about the other freedoms that they treasure so much," Mr Tai said.
Hong Kong is one of the few parts of China where open protests are allowed and pro-democracy activists will be using the July 1 anniversary of the handover to call for swifter electoral reforms. Last year's event attracted an estimated 430,000 protesters, according to organisers.
Occupy Central has also threatened to paralyse Hong Kong's financial district with thousands of protesters at the end of the year if officials do not allow voters to choose their own candidates.
Mr Tai said the numbers taking part in the unofficial referendum would bolster the case for reform. "Having a good turnout is good, because then we might have a stronger bargaining power at a later stage of negotiation," he said.
The vote comes as concerns grow that the civil liberties enjoyed by Hong Kong - guaranteed until 2047 under the "one country, two systems" agreement - are being steadily eroded.
Beijing's cabinet last week published a white paper reasserting China's control over Hong Kong, triggering angry protests in the city. It was China's first ever policy document stipulating how Hong Kong should be governed, in what was widely interpreted as a warning for Hong Kong not to overstep its boundaries.