Protesters calling for full democracy in Hong Kong vowed Thursday to ratchet up their occupation of key parts of the city if they fail to win concessions from the government ahead of crunch talks tomorrow.

The threat was issued as the city's embattled leader came under pressure to explain why he kept large payments from an Australian company secret with pro-democracy lawmakers saying they would try to impeach him.

Parts of the vital financial hub have been paralysed for more than a week by demonstrations calling for Beijing to grant the former British colony full democracy and for the city's Chief Executive Leung Chun-ying to resign.

Under plans unveiled by China in August, Hong Kongers will be able to vote for Leung's successor in 2017, but only two to three vetted candidates will be allowed to stand.

Although protester numbers have dwindled in recent days, small groups still control multiple barricades across the city in what has become the most concerted challenge to Beijing's rule since Hong Kong's handover in 1997.

In a show of unity Thursday evening, a coalition of pro-democracy leaders gathered at the main protest site and vowed to ratchet up their civil disobedience campaign unless the government agreed to their demands.

Students are due to meet Leung's deputy Carrie Lam on Friday afternoon in bid to break the deadlock.

But Alex Chow, president of the Hong Kong Federation of Students, said pro-democracy protesters would remain on their barricades -- and could expand their occupation -- if the talks broke down.

"Hong Kong people will not retreat. And there's no reason for anyone to ask us to retreat. Therefore the Occupy movement must be ongoing," he said.

"Also the students will go into different occupy areas," to discuss potential future plans for further civil disobedience, he added.

Pro-democracy lawmakers also threw their weight behind the protests Thursday saying they would use their powers to disrupt the workings of the Hong Kong government inside the city's parliament by gridlocking the committees they they currently control.

"Hong Kong has entered an era of disobedience and non-cooperation," pro-democracy leader Alan Leong told crowds.

His call came as lawmakers accused the city's leader of having a "huge integrity problem" for failing to declare a lucrative windfall of cash from business dealings in Australia.

Fairfax Media reported Wednesday that Leung received two payments totalling HK$50 million ($6.5 million) from Australian engineering firm UGL during a deal struck in December 2011 -- months before the chief executive took office, but a week after he announced his candidacy.

At the time UGL was purchasing the insolvent property services firm DTZ, where Leung was a director and chairman of its regional operations.

It agreed to pay Leung over the next two years not to compete with them, and the contract signed by him showed he agreed to act as an "adviser from time to time".

Opposition lawmakers Thursday expressed their dismay that Leung did not declare the payments to the Hong Kong public once he became leader in July 2012.

"It boils down to a huge integrity problem," pro-democracy lawmaker Claudia Mo told AFP. "Can you imagine Obama being a consultant of some company while being a political leader?"

Leung's office has said he was under no legal obligation to declare the earnings and that he had not worked for UGL since becoming chief executive.

Pro-democracy lawmaker Leong said his group of 23 lawmakers in the 70-seat body were planning to file an impeachment order against the chief executive following the emergence of the deal.

"We are gathering the evidence and working on the draft. We will move the motion in the Legco when the draft is ready," Leong said.