Violent clashes erupted early on Sunday in a Hong Kong protest hotspot as unarmed pro-democracy activists once again confronted riot police despite the confirmation of talks between protest leaders and officials early this week.

Hong Kong's 28,000 strong police force have been struggling to contain a youth-led movement that has shown little sign of waning after three weeks of standoffs in which hundreds of thousands of people have occupied city streets to demand full democracy in the former British colony.

In the densely populated Mong Kok district, police managed to earlier repel protesters from a major intersection but have faced a significant pushback.

In the early hours of Sunday, demonstrators launched a fresh midnight assault, suddenly putting on helmets and goggles to ready themselves, before surging forward to grab a line of metal barricades hemming them into a section of road.

Amid screams and cursing, hundreds of officers began whacking the protesters who raised a wall of umbrellas. Pepper spray was used intermittently amid violent scuffles. The police then surged forward with riot shields, forcing protesters back.

Hong Kong protests

Riot police clash with pro-democracy protesters at the Mong kok shopping district of Hong Kong on Sunday morning. (Carlos Barria/Reuters)

"Black Police! Black Police!" the crowds shouted amid the fray. One protester in a white T-shirt and goggles was beaten by a flurry of batons leaving him bleeding from a gash in the head. Several protesters were taken away. Fire trucks with water cannons were stationed further down the street but weren't used.

A senior policeman on the scene, Paul Renouf, said 400 to 500 officers were deployed to force the crowds around 20 metres back from their original position near a key intersection.

Hong Kong's Security Chief Lai Tung-kwok said some of the clashes in recent days had been initiated by activists affiliated to "radical organizations which have been active in conspiring, planning and charging violent acts".

The fresh street battles come just hours after Hong Kong's pro-Beijing leader Leung Chun-ying offered talks to student leaders next Tuesday in an attempt to defuse the three-week long protests that have grabbed global headlines with scenes of clashes and tear gas rising between waterfront skyscrapers.

Leung's chief secretary, Carrie Lam, announced on Saturday that talks between student leaders and the city government would take place for two hours on Tuesday and be broadcast live.

The protests have been going on for three weeks and pose one of the biggest challenges for China since the crushing of pro-democracy demonstrations in Beijing in 1989. It is also the gravest governance crisis faced by Hong Kong's government since the 1997 handover to China, with no clear resolution in sight.

"These illegal acts are undermining the rule of law, undermining (what) Hong Kong has been relying on to succeed," said Police Commissioner Andy Tsang. He added his force had been "extremely tolerant" but had failed to prevent the demonstrations becoming more "radical or violent".

Chinese and Hong Kong leaders are refusing to give in to any protesters' demands, while the movement has so far been galvanized, rather than cowed, by the use of police force.

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 colony which returned to Chinese rule in 1997.

Mong kok is a protest hotspot

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

But Beijing ruled on Aug. 31 it would screen candidates who want to run for the city's chief executive in 2017, which democracy activists said rendered the universal suffrage concept meaningless. The protesters are demanding free elections for their leader.

The Mong Kok area known for its tough, working class social fabric and criminal underbelly, has been the scene of violent brawls in recent weeks, pitting students against hostile mobs including triads, or local gangsters. While the heart of the protest zone was cleared away in the early hours of Friday, protesters regrouped to take back key sections within 24 hours.

Posters declaring "Reclaim Mong Kok!" had been plastered on shop fronts.

"We'll keep coming back," said student Angel So, 20, as a friend, Terry Leung, nursed grazes on his arms and legs from scuffles with police.

Besides Mong Kok, about 1,000 protesters remained camped out on Hong Kong Island in a sea of tents on an eight-lane highway beneath skyscrapers close to government headquarters.