Hong Kong police battling pro-democracy activists for control of an underpass have sparked public anger after officers were seen kicking a handcuffed protester.
In the worst violence since street demonstrations for greater democracy began more than two weeks ago, officers armed with riot shields, batons and pepper spray knocked activists to the ground, dragged dozens away and tore down barricades protesters used as roadblocks around the underpass outside the government's headquarters.
Outrage over their aggressive tactics exploded after local TV showed half a dozen officers taking the protester around a dark corner and kicking him on the ground. It is unclear what provoked the attack.
Local Now TV had shown footage of him splashing water on officers beforehand.
Pro-democracy politician Lee Cheuk-yan said: "Hong Kong police have gone insane today, carrying out their own punishment in private.
"Hong Kong's values and its rule of law really have been completely destroyed by police chiefs."
Beijing, meanwhile, issued its harshest condemnations yet of the protests, calling them illegal, bad for business and against Hong Kong's best interests.
The central government has become increasingly impatient with the demonstrations, the biggest challenge to Beijing's authority since China took control of the former British colony in 1997.
A front-page editorial in the People's Daily, the ruling Communist Party's mouthpiece, condemned the protests and said "they are doomed to fail".
"Facts and history tell us that radical and illegal acts that got their way only result in more severe illegal activities, exacerbating disorder and turmoil," the commentary said.
"Stability is bliss, and turmoil brings havoc," it said.
However, there were no signs that the central government was planning to become directly involved in suppressing the demonstrations, which have marshalled opposition to plans for a pro-Beijing committee to screen candidates to run in Hong Kong's first elections to choose the city's chief executive in 2017.
The protesters also want the current leader, the deeply unpopular Leung Chun-ying, to resign.
The demonstrations have posed an unprecedented challenge to the government, and it is unclear when and how the crisis will be resolved.
Mr Leung, who described the protests as being "out of control," told reporters that officials are willing to talk to protesters, but reiterated that Beijing will not drop the election restrictions it imposed.
He cancelled a leader's questions session at the Legislative Council scheduled for Thursday, citing security risks.
The police operation came hours after a large group of protesters blockaded the underpass, expanding their protest zone after being cleared out of some other streets.
The protesters outnumbered the police officers, who later returned with reinforcements to clear the area.
The underpass borders the city government headquarters and is close to the main protest zone straddling a highway on the opposite side of the complex.
Demonstrators appeared to storm the short tunnel in reaction to police attempts over the past two days to remove barricades on the edges of the sprawling protest zone.
Police said they had to disperse the protesters because they were disrupting public order and gathering illegally. They arrested 45 demonstrators, none of whom were injured, a police spokesman said.
But local television channel TVB showed footage of around six plainclothes police officers taking a man around the side of a building, pushing him to the ground and kicking him. Local legislators and activists identified the protester as Ken Tsang, a member of a local pro-democracy political party.
Secretary for security Lai Tung-kwok told reporters that the officers who were involved have been temporarily reassigned and the police department is carrying out an investigation.
Mr Tsang, through his lawyer Tanya Chan, alleged that officers also slapped him after he was taken to a police station. Activists circulated photos of bruises on his face and back.
Protester Simon Lam said: "Some of us were sleeping in the park when more than a hundred of them ran toward us with torches as if they're trying to blind us temporarily. We were not prepared for how aggressive they were."
After initial attempts to disperse protesters with tear gas and pepper spray two weeks ago, police have adopted a different strategy of chipping away at the three protest zones by removing barricades from the edges of the occupied areas in the early morning, when the crowd numbers are usually lowest.
But Wednesday's raid was the most violent so far, with police charging the protesters and dragging them away.
One officer ripped a facemask off a male activist before spraying him with pepper spray, according to a video on the South China Morning Post newspaper's website.
Positions on both sides have been hardening since the government called off negotiations last week, citing the unlikelihood of a constructive outcome given their sharp differences.
Beijing is eager to end the protests to avoid emboldening activists and others on the mainland seen as a threat to the Communist Party's monopoly on power.
Zhang Xiaoming, director of the central government's liaison office in Hong Kong, was quoted as telling Hong Kong legislators at a banquet that the protest movement "is a serious social and political incident".
Mr Zhang said the movement challenged Beijing's authority and had caused the city to suffer huge economic losses. They had "hurt the basis of Hong Kong's rule of law, democratic development, social harmony, international image and its relations with the mainland," he said.
Mr Zhang called for an end to the protests as soon as possible to avoid further losses to Hong Kong's citizenry as a whole.
Mr Lam, the student protester, said he feared tensions will keep escalating as students' distrust of police grows.
"Now there is a feeling we are not just here to fool around or just to sit peacefully. We are feeling more prepared. We have become more united in building defences," he said.
The protester, Ken Tsang, said officers assaulted him while he was "detained and defenseless," and that he was attacked again in the police station afterwards.
Mr Tsang, a member of a pro-democracy political party, showed reporters injuries to his torso and said he is considering legal action against police.
Police spokesman Steve Hui said seven officers who were involved have been temporarily reassigned, and that authorities will carry out an impartial investigation.
Police arrested 45 demonstrators during the clashes, and said five officers were injured.