Clashes have taken place between Hong Kong police and a small group of protesters who tried to break into parliament early on Wednesday.
Protesters used metal barricades to break down a side door at the Legislative Council building (Legco).
The incident happened hours after bailiffs and police peacefully cleared a section of the main protest camp.
Protesters calling for full democracy have occupied three key sites in Hong Kong for nearly eight weeks.
The BBC's John Sudworth in Hong Kong said that this latest incident was a reminder that the overwhelmingly peaceful protests can still turn ugly.
Dozens of young protesters, some wearing masks, tried smashing in the door shortly after 01:00. Some reportedly managed to enter the building.
Riot police warned protesters to stay back, using red flags, and later used pepper spray to push them back.
There were repeated attempts by protesters to enter the building throughout the night, but they appeared to retreat by daylight.
Police officers use pepper spray to stop the pro-democracy protesters breaking into the Legislative Council in Hong Kong early Wednesday, 19 November 2014.
Police used pepper spray and batons to push back the protesters
Protesters tried smashing in the door with concrete slabs, metal objects and rocks
Democratic lawmaker Fernando Cheung, who was among a group of people who tried to stop the protesters, told Reuters: "This is a very, very isolated incident. I think it's very unfortunate and this is something we don't want to see happen because the movement so far has been very peaceful."
The South China Morning Post reported that police had arrested four people.
Some protesters told the newspaper that they had attempted the break-in because they were angry about the earlier clearance of part of the main protest site at Admiralty.
Tuesday's clearance in front of Citic Tower came after the building's owners were granted an injunction by the high court.
An injunction has also been granted for the clearance of roads at the Mong Kok protest site. The Post says hundreds of police are on standby to clear that site as early as Thursday. A third protest site remains at Causeway Bay.
The protesters have been on the streets since early October to demonstrate against a decision by China to screen candidates for Hong Kong's 2017 leadership election. Numbers were originally in the tens of thousands but have fallen to a few hundred.
Hong Kong and the Beijing government say the protests are illegal, and there is growing public frustration with the disruption to traffic and business.
Police operations to clear and contain the camps in recent weeks have sometimes led to clashes. An earlier attempt to clear an underpass near Admiralty led to accusations that police had used excessive force, after a video emerged of officers apparently beating a protester.
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