Violent clashes erupted in Hong Kong early on Sunday 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 two hours on Tuesday 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 standoff worsen and getting violent," Sonny Lo, a professor at the Hong Kong Institute of Education, told Reuters.
"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 standoffs.
Demonstrators in the Mong Kok district launched a fresh assault early on Sunday, putting on helmets and goggles before surging forward to grab a line of metal barricades hemming them into a section of road.
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, leaving him bleeding from a gash in the head. Several protesters were taken away. Fire trucks with water cannons were stationed along the street but were not used.
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.
The clashes came hours after Hong Kong's pro-Beijing leader Leung Chun-ying called for the talks on Tuesday. 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 Aug. 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.
Hong Kong's Security Chief Lai Tung-kwok said some of the clashes in recent days had been initiated by activists affiliated to "radical organisations which have been active in conspiring, planning and charging violent acts."
The city's embattled police chief, Andy Tsang, also expressed his frustration when he broke three weeks of silence on Saturday to say "extremely tolerant" policing had not stopped protests becoming more "radical or violent."
Senior police officials and their unions are warning that front-line officers are facing immense stress.
The demonstrations pose one of the biggest challenges for China since the crushing of a pro-democracy movement in Beijing in 1989.
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Protesters resting during the day on Sunday were defiant and also angry that the city government was portraying their campaign as increasingly radicalised and violent.
Lap Cheung, 40, said he quit his IT job in the United States to return to Hong Kong to join the protests when he heard a student leader had been arrested three weeks ago.
"I will continue to stay here until CY (Leung) resigns," he said, adding that he had no hope for Tuesday's talks.
Student Igloo Novas said Hong Kong leaders must tell Beijing the "truth," that the majority of Hong Kong people wanted to freely choose candidates in elections.
"This is one compromise I can accept from the government," she said.
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.