Hong Kong's democracy activists are planning a street vote to gauge protesters' views on conciliatory offers from the government, as the city's former leader on Friday called on them to clear the streets.

The leaders of the mass demonstrations that have paralysed parts of the city for nearly a month said they will poll demonstrators at the main protest camp opposite government headquarters on Sunday evening.

During face-to-face talks Tuesday with student leaders, government negotiators offered to write a report to Beijing detailing protester sentiments.

They also suggested both sides could set up a joint committee to discuss further political reform beyond the next leadership elections in 2017.

The student leaders initially dismissed the offers as lacking substance but have since decided to conduct a straw poll of voters to decide on their next move.

Details on the poll and how it will be conducted -- including whether it will be extended to the two other protest sites in the Mongkok and Causeway Bay districts -- are expected later Friday, protest groups said.

"The poll can quantify opinions and tell the government that people in different occupied areas are requesting the government to come up with a practical response," protest leader Alex Chow told reporters.

Plans for the vote came as former leader Tung Chee-hwa called the protests a "gross violation", warning that the consequences of continuing the rallies beyond a month were "very serious".

Tung was Hong Kong's first chief executive after the 1997 handover and was himself ousted after huge protests.

"We need to end this occupation because not only... is it hurting the livelihood of people but it's a gross violation of the law," Tung told reporters in his first public comments since the protests began nearly four weeks ago.

"One month is a long time already and the consequences of prolonging this occupation is very, very serious," he said of the movement's impact on the city's economy.

One pro-democracy lawmaker dismissed Tung's comments, saying they would have little impact on predominantly young protesters who have no respect for a former leader known for his consistently pro-Beijing politics.

"They (the government) are acting out of desperation if they felt Tung Chee-hwa just might command some moral or ideological authority over the general population here. That's more than a myth, it's just a joke," lawmaker Claudia Mo told AFP.

Tung also lent his support to the city's embattled leader Leung Chun-ying.

"During this time where there are many risks, I feel he has performed very well and has also gained the trust of the Chinese government," he said

Tung had his own share of troubles in handling pro-democracy protests when 500,000 people took part in a rally against a proposed national security bill in 2003, forcing his administration to shelve it.

It was a key factor in his resignation eighteen months later.

Shortly after Tung spoke, fresh scuffles broke out between protesters and a group of masked men who tried to pull down barricades in Mongkok.

The densely packed working-class district has previously seen some of the worst violence during the protest movement and has regularly been attacked by angry locals.

Demonstrator positions had paint and faeces thrown at them from apartment roofs overlooking the protest site earlier in the week. (AFP)