Hong Kong protesters clashed with dozens of police using batons and pepper spray early Wednesday, in some of the worst violence since pro-democracy demonstrations began more than two weeks ago.

The confrontation broke out during a police operation to clear newly erected barricades on a main road next to the city's embattled government headquarters.

A wall of police armed with shields and batons marched before dawn on crowds clutching the umbrellas that have become emblematic of their fight for full democracy.

Police used their fists and batons to beat back protesters who refused to retreat, aiming pepper spray in their faces in wild scenes.

Others were pulled to the ground, handcuffed and hauled away by officers, and there were injuries on both sides. Police said that 45 people had been arrested in the operation, including 37 men and eight women.

Within an hour police had regained control of Lung Wo Road, which sits just metres from the offices of Hong Kong's Chief Executive Leung Chin-Ying, ending a short-lived occupation that protesters staged the day before.

The violence was among the worst seen since the start of rallies that have drawn huge crowds calling for Beijing to grant the semi-autonomous city the right to hold free elections.

China has insisted it will vet candidates standing for election as the semi-autonomous city's next leader in 2017 -- a move protesters deride as "fake democracy".

While the activists have been praised for their civility and organisational skills, they have also brought widespread disruption and traffic congestion to the financial hub, and tempers on all sides have begun to fray.

'Emotions are very unstable'

A police statement said officers had warned that "advancing against police cordon line even with their arms raised is not a peaceful act", and had appealed to the demonstrators to "stay calm and restrained".

Ben Ng, an 18-year-old student, was with protesters near a newly built barricade when the baton-wielding contingent approached.

"Police used pepper spray without any threat or warning. Protesters were beaten by police," he said. "Both protesters and police, their emotions are very unstable."

Journalists were also jostled by security forces and warned they would not be treated any differently if they breached a cordon.

"(Police) grabbed me, more than 10 police, and they beat me, punches, kicks, elbows. I tried to tell them I'm a reporter but they didn't listen," Daniel Cheng, a reporter for an online news portal, told AFP.

Cheng, who suffered cuts to his lip and bruises on his neck and back, said he was later released after showing his press card.

Tearing down barricades

The protests that have paralysed parts of the city over the last fortnight have largely been peaceful. But ugly scuffles have frequently broken out between demonstrators and government loyalists, sparking accusations the authorities are using hired thugs.

Patience is running short in some quarters, with shop owners and taxi drivers losing business and commuters voicing irritation at extensive disruptions on the roads and on public transport.

Direct confrontation with police has been much less common, however. Wednesday's running battles were some of the most serious since September 28, when riot police fired tear gas at largely peaceful crowds.

In the last two days, officers have begun swooping in to remove barricades on the edges of protest sites in the city, shrinking their footprint and opening some roads to traffic, while allowing the bulk of demonstrators to stay in place.

A new poll released Tuesday by Hong Kong University showed Leung's support rating dropped 2.6 percent from late last month to 40.6 percent, his second-lowest rating since he came to office in 2012.

Protest leader Alex Chow on Tuesday reiterated a call for Leung -- whose resignation protesters are demanding -- to restart stalled talks after the government abruptly cancelled a dialogue last week.