Violent clashes erupted in Hong Kong for a second night, deepening a sense of impasse between a government with limited options and a pro-democracy movement increasingly willing to confront police.

The worst political crisis in Hong Kong since Britain handed the free-wheeling capitalist city back to China in 1997 entered its fourth week with no sign of a resolution despite talks scheduled for tomorrow between the government and student protest leaders.

Beijing has signalled through Hong Kong's leaders that it is not willing to reverse a decision in August that effectively denies the financial hub the full democracy the protesters are demanding.

"Unless there is some kind of breakthrough in two hours of talks on Tuesday, I'm worried we will see the stand-off worsen and get violent," Sonny Lo, a professor at the Hong Kong Institute of Education said.

"We could be entering a new and much more problematic stage. I hope the government has worked out some compromises, because things could get very difficult now."

Hong Kong's 28,000-strong police have been struggling to contain a youth-led movement that has shown little sign of waning after three weeks of stand-offs.

Demonstrators in the Mong Kok district launched a fresh assault early yesterday, putting on helmets and goggles before surging forward to grab a line of metal barricades, hemming them in.

Hundreds of police officers hit out at a wall of umbrellas that protesters raised to fend off police pepper spray. Protesters screamed and hurled insults and violent scuffles erupted before police surged forward with riot shields, forcing the protesters back.

"Black Police! Black Police!" protesters shouted. One activist in a white T-shirt and goggles was hit with a flurry of baton blows. Several protesters were taken away.

Senior policeman at the scene Paul Renouf said 400 to 500 officers were deployed to force the crowds about 20 metres back from their original position near an intersection. Dozens of people were reportedly injured in the two nights of clashes, including 22 police officers. Four people were arrested early yesterday, police said.

The clashes came hours after Hong Kong's pro-Beijing leader Leung Chun-ying called for the new talks. They will be broadcast live.

The protesters, led by a restive generation of students, have been demanding China's Communist Party rulers live up to constitutional promises to grant full democracy to the former British trading outpost.

Hong Kong is ruled under a "one country, two systems" formula that allows it wide-ranging autonomy and freedoms and specifies universal suffrage for Hong Kong as an eventual goal.

But Beijing is wary about copycat demands for reform on the mainland and it ruled on August 31 it would screen candidates who want to run for the city's chief executive in 2017.

Democracy activists said that rendered the universal suffrage concept meaningless. They are demanding free elections.

Leung appears hamstrung, unable to compromise because of the message that would send to people on the mainland, while more force looks likely to only galvanize the young protesters.