The police operation was the toughest against largely student protesters in more than a week, and came after demonstrators swarmed into a tunnel on a key four-lane thoroughfare late on Tuesday, halting traffic and chanting for universal suffrage in the Chinese-controlled city.
Hundreds of police forced the crowds back, using pepper spray on those who refused to move.
Several protesters were wrestled to the ground and taken away. Scores of other officers then entered the tunnel in the Admiralty district near government headquarters and cleared away makeshift walls formed from concrete slabs, reopening the tunnel to traffic.
Local media said 45 people had been arrested overnight.
Footage aired on Hong Kong television showed police kicking and beating one protester for several minutes. Police could not immediately be reached for comment.

"There were so many police. They punched people ... We are peaceful," Danny Chiu, a student in his 20s,said breaking down in tears.
By mid-morning on Wednesday police had largely left the area.
Protesters have been demanding full democracy for the former British colony in the wake of restrictions placed by China on the city's next elections in 2017. They are also calling for Hong Kong's embattled leader, Leung Chun-ying, to step down.
But their campaign, now into its third week, has caused traffic chaos and drained public support for their actions.
China rules Hong Kong under a 'one country, two systems' formula that accords the city a degree of autonomy and freedom not enjoyed in mainland China, with universal suffrage an eventual goal.
Beijing said on 31st August that only candidates that get majority backing from a nominating committee stacked with Beijing loyalists would be able to contest a full city-wide vote to choose Hong Kong's next leader.
China's ruling Communist Party believes it has offered enough concessions to Hong Kong in the past, and would give no ground to the protesters because it wants to avoid setting a precedent for reform on the mainland.
The position was arrived at during a meeting of the new National Security Commission chaired by President Xi Jinping in the first week of October, the sources said.
On Tuesday, police used chainsaws and sledge-hammers to clear blockades on another major road in Admiralty.

But hundreds of protesters then stormed into the nearby tunnel, catching authorities by surprise.

The tunnel on Lung Wo Road, an important east-west artery near the offices of the government and legislature, had been intentionally left open by demonstrators to traffic.

Despite the reopening of the two major roads to ease what police said was traffic congestion, there was no immediate sign the core protest zone outside government headquarters, where hundreds of tents remain pitched on an eight-lane highway, would be cleared. Protesters are also loosely scattered around other parts of the Admiralty district.
Protesters had earlier erected a gravestone in the middle of Lung Wo Road for Leung. 'Even hell won't welcome you' read an epitaph on the makeshift headstone.

The pro-Beijing leader said this week there was 'zero chance' China's leaders would give in to protesters' demands and change the August decision limiting democracy.

The Hong Kong and Beijing governments have called the protests illegal. Some of the city's most powerful tycoons had earlier warned that occupying the heart of the city to press for democracy could undermine stability.
They have remained largely silent since the protests began.
Police, criticized for using tear gas and batons in the first 24 hours of the protests, have adopted a more patient approach, counting on protesters to come under public pressure to clear main arteries. In recent days, police have selectively removed some barriers on the fringes of protest sites.
The police action in the early hours of Wednesday, however, suggests official patience may be wearing thin.
The number of protesters has fallen off sharply from a peak of about 100,000, but a hardcore group of perhaps several thousand remain.
"The protestors having endured the attacks by the anti-occupy people, I don't think they will just surrender unconditionally and leave," said Joseph Wong, political analyst at the University of Hong Kong.

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