Hong Kong police have used tear gas, rubber bullets and water cannon to disperse crowds as tens of thousands marched in the city, defying a ban.
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 China’s special administrative region.
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.