Hong Kong's pro-democracy protesters were Sunday forced to suspend a planned vote on their next steps -- hours before it was due to begin -- due to differing opinions about how to move their month-long campaign forward.

Four weeks after tens of thousands of Hong Kongers took to the streets demanding free leadership elections for the semi-autonomous Chinese city, protesters remain stubbornly encamped across several major road junctions.

But the crowds have shrunk dramatically and their leaders have struggled to decide how to keep up the momentum.

With Beijing insisting that candidates for the 2017 vote must be vetted by a loyalist committee -- an arrangement the protesters deride as "fake democracy -- there is no end to the stalemate in sight.

The vote by mobile phone had been set to take place on Sunday and Monday evening to gauge protesters' opinions on what their next moves should be.

But just hours before voting was due to begin, protest leaders told reporters they had been forced to postpone it because of differing views on how it should be carried out.

"We decided to adjourn the vote... but it doesn't mean the movement has stopped," said Benny Tai of prominent pro-democracy group Occupy Central, adding it was a "very difficult decision to make".


Retreat ruled out

Organisers bowed in apology for disappointing supporters of a movement that has come to be known as the "umbrella revolution", after the umbrellas wielded by demonstrators in the face of police tear gas.

"There have been a lot of conflicts and different opinions," student leader Alex Chow told reporters.

Organisers refused to be drawn on the nature of the disagreements, but Chow said there had been concerns over how to verify that only protesters took part in the vote, amid worries that opponents might try to hijack the process.

The vote had been due to take place at the three protest camps that have sprung up across Hong Kong. It would have asked demonstrators how to respond to conciliatory measures offered by Hong Kong's government.

The government made tentative concessions during talks last Tuesday, offering to file a report to Beijing about recent events and suggesting that both sides set up a committee to discuss further political reform beyond 2017.

With frustration growing among residents after a month of traffic mayhem caused by the protests, and sporadic clashes breaking out with police and opponents, the pro-democracy movement is under growing pressure to decide where it is headed next.

In the latest ugly scenes, four journalists were attacked by angry pro-government demonstrators on Saturday evening at a counter-rally calling for the democracy protesters to go home.

But protest leaders on Sunday offered few clues on how they would proceed now -- refusing to say even whether the vote would be rescheduled.

"At this stage of the movement every one of us is exploring which way to go," Benny Tai told reporters.

"We need to have more discussions," he said, adding that discussions would include whether to hold a broader referendum on democratic reforms.

Protest leaders said a retreat was the only option that could be ruled out, with student activist Joshua Wong saying it was "absolutely not the time" to quit the streets.

More than a thousand protesters gathered on Sunday at the main protest camp in Admiralty outside government headquarters, listening to speeches at the colourful tent city that has sprung up on the highway there.

A former British colony, Hong Kong was handed back to China in 1997 under a "one country, two systems" deal which guarantees civil liberties not seen on the mainland, including freedom of speech and the right to protest.

But concerns have been growing that these freedoms are being eroded, while frustrations have also been building over growing inequality in the freewheeling financial hub.

The protests come as one of the biggest challenges to Beijing's authority since the Tiananmen protests of 1989.