Forty-five people have been arrested in Hong Kong after police and demonstrators clashed, with dozens of officers in riot gear using pepper spray in some of the most violent scenes since protests against the government.

Police early on Wednesday also used batons to beat back protesters guarding newly erected barricades on a main road next to the city's embattled government headquarters.

Al Jazeera's Sarah Clarke, reporting from Hong Kong, said: "The police presence has been much higher today [Wednesday]. The public has been denied access to the main thoroughfare. This is where it all happened last night."

Meanwhile, six police officers were removed from their posts and reassigned after footage of the officers in plain clothes beating up a protester, shown on local television channels.

Police have promised an impartial investigation into the incident.

The city centre has been the scene of intermittent rallies drawing huge crowds calling for Beijing to grant the semi-autonomous city the right to hold unfettered leadership elections.

While the activists have been praised for their civility and organisational skills, they have also brought widespread disruption to the financial hub, especially to key traffic arteries on Hong Kong's main island.

A wall of police marched on Wednesday against demonstrators clutching the umbrellas that have become emblematic of their fight for full democracy in the financial hub, striking protesters and shoving them to the ground.

Protesters alleged that pepper spray was used indiscriminately and without warning.

Within an hour police had regained control of Lung Wo road, which sits just metres from the offices of Hong Kong's embattled Chief Executive Leung Chun-Ying and which was occupied by protesters earlier on Tuesday.

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

Young protesters are vowing to continue occupying the streets. Students are planning another protest march that will happen in response to the police crackdown.

"If we keep occupying different streets, this may give some pressure to them [the government], because they cannot control us," Samuel Lam, a 22-year-old pro-democracy protester told the Reuters news agency.

Tearing down barricades

Late on Tuesday, protesters told the AFP news agency that they had decided to take over the highway - which had previously been unoccupied by activists - after police cleared another main road near the central Admiralty protest site without warning.

Protesters moved metal barricades inside a tunnel on the road, which runs east-west outside the government complex.

The protests that have paralysed parts of the city over the last fortnight have largely been peaceful.

But angry and sometimes violent scuffles have frequently broken out between demonstrators and government loyalists, sparking accusations that the authorities are using hired thugs.

Tempers are fraying, with shop owners and taxi drivers losing lucrative business, and commuters voicing irritation at their disrupted journeys to work.

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.

Source: Al Jazeera and agencies