Hong Kong police have arrested four men as tensions once again flared after a small group of protesters broke into the city’s legislature through a side door.

The arrest on Wednesday came a day after court bailiffs managed to clear part of a protest camp in the heart of the city that has been occupied by demonstrators for nearly two months, while leaving most of the main protest site intact.

About 100 riot police with helmets, batons and shields stood guard outside the government building in the early hours of Wednesday, facing off with protesters who are demanding free elections for the city's next leader in 2017.

"Police retreat!" the protesters chanted.

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It was the first time protesters had broken into a key public building, defying the expectations of many political analysts who had predicted that Hong Kong's most tenacious and protracted protest movement would slowly wind down.

The escalation came in the early hours of Wednesday when a small group of protesters charged towards the legislature and used metal barricades and concrete tiles to ram a glass side door. They eventually smashed through, with several managing to get inside, according to witnesses.

Fernando Cheung, a lawmaker, said he and other protesters had tried to stop the small group of radical activists from breaking through. "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," he said.

Hong Kong was returned to China from British colonial rule in 1997 under a "one country, two systems" formula that gives the city more autonomy and freedom than the mainland, with an eventual goal of universal suffrage.

The protesters are demanding open nominations in the city's next election for chief executive in 2017. Beijing has said it will allow a vote in 2017, but only between pre-screened candidates. 

Source: Agencies