Police fired a water cannon and tear gas at protesters who lobbed petrol bombs outside the Hong Kong government office complex as violence flared anew after thousands of pro-democracy supporters marched in defiance of a police ban.
A mixed crowd of hardcore protesters in black and wearing masks, along with families with children, spilled into the roads of the Causeway Bay shopping belt and marched for over 2km to the central business district.
Some waved US and British flags, while others carried posters reiterating their calls for democratic reforms.
Police had turned down a request by the Civil Human Rights Front to hold the march, but the demonstrators were undeterred, as they have been all summer.
"I feel this is our duty. The government wants to block us with the ban, but I want to say that the people will not be afraid," said one protester, Winnie Leung, 50.
Many shops closed their doors. Some protesters used traffic cones, metal fencing and rubbish bins to set up road barriers.
Protesters burned Chinese flags and tore down banners congratulating China's ruling Communist Party, which will celebrate its 70th year in power on October 1.
In familiar scenes, some protesters smashed glass windows and surveillance cameras at a subway station exit.
Hundreds of protesters later targeted the government office complex, throwing bricks and petrol bombs through police barriers. Police responded by firing volleys of tear gas and using a water cannon truck to spray chemical-laced water, in a repeat of confrontational scenes from the last few weeks of the protests.
Police had earlier warned in a statement that the assembly was illegal and urged protesters to "stop their illegal acts."
The protests were triggered in June by an extradition bill that many saw as an example of China's increasing intrusion and at chipping away at Hong Kong residents' freedoms and rights, many of which are not accorded to people in mainland China.
Hong Kong's government promised this month to withdraw the bill, which would have allowed some criminal suspects to be sent to mainland China for trial, but protesters have widened their demands to include direct elections for the city's leaders and police accountability.
More than 1300 people have been arrested since the protests started.
Beijing has accused foreign powers of fomenting the unrest.
Earlier Sunday, hundreds of protesters waved British flags, sang "God Save the Queen" and chanted "UK save Hong Kong" outside the British Consulate as they stepped up calls for international support for their campaign.
They repeated calls for Hong Kong's former colonial ruler to ensure the city's autonomy is upheld under agreements made when it ceded power to China in 1997.