REPUBLIKA.CO.ID, HONG KONG -- Carrying banners and chanting slogans, thousands of protesters gathered Tuesday for a pro-democracy rally in Hong Kong that organisers say could be the largest since the city was handed back to China.

The rally reflects surging discontent over Beijing's insistence that it vet candidates before a vote in 2017 for the semi-autonomous city's next leader.

The march comes after nearly 800,000 people voted in an informal referendum demanding a electoral mechanism that allows voters to nominate candidates.

The poll has irked Beijing, which branded it "illegal and invalid" despite the unexpectedly high turnout.

The city's Victoria Park, the starting point of the march that will culminate in the skyscraper-packed Central business district, was a sea of umbrellas as well as banners bearing slogans such as "We want real democracy" and "Civil nominations for all".

Some protesters sang the Cantonese version of "Do You Hear the People Sing?" -- the anthem from the musical and film "Les Miserables".

"Hong Kong is turning into a place with less and less freedom," Eric Wong, a 24-year-old photographer who took part in the rally, told AFP. "It is transforming into the mainland."

Organisers expect more than half a million people to join the rally -- a record high.

Paul Yip, a statistician at Hong Kong University, told the South China Morning Post he was leading a team of 10 to independently assess the crowd size, a topic of great politically sensitivity.

July 1, a traditional day of protest in Hong Kong, marks the anniversary of its handover from Britain to China in 1997 under a "One country, two systems" agreement.

That allows residents liberties not seen on the mainland, including free speech and the right to protest.

But there are heightened fears that those freedoms are being eroded.

There has been a spate of attacks on media workers in recent months -- including the stabbing of a liberal former newspaper editor -- while pro-democracy media have complained of massive cyber-attacks.

Concerns increased in June when Beijing published a controversial "white paper" on Hong Kong's future that was widely seen as a warning to the city not to overstep its boundaries.

"Public sentiment has dropped to the lowest point since 2003. I believe more people will come out," Johnson Yeung, one of the key rally organisers, told AFP.

The 2003 march saw 500,000 people protest against a proposed national security bill, forcing the government to shelve it.

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