Demonstrators lit fires, threw petrol bombs at riot police and attacked the parliament building.
An event to mark five years since Beijing ruled out fully democratic elections was banned in Hong Kong, a special administrative region of China.
On Friday, several key pro-democracy activists and lawmakers were arrested.
The protest movement grew out of rallies against a controversial extradition bill - now suspended - which would have allowed criminal suspects to be sent to mainland China for trial.
It has since become a broader pro-democracy movement in which clashes have grown more violent.
BBC
More about: HongKong
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