Hong Kong protesters flooded the city's streets on Sunday in defiance of a ban by the authorities on their march, setting up roadblocks and tossing firebombs amid the firing of tear gas by police.
Protest leaders pressed their calls for accountability and political rights.
Police had beefed up security measures for the unauthorized rally, the latest in the unrest that has disrupted life in the semi-autonomous Chinese territory since early June.
Black-clad and masked protesters barricaded streets at multiple locations in Kowloon, where the city's subway operator restricted passenger access.
A firebomb was tossed at one subway station.
The protesters tore off stones from the sidewalk and scattered them on the road, commandeered plastic safety barriers and unscrewed metal railings to form makeshift roadblocks.
Police fired tear gas after gasoline bombs were thrown toward one subway station as tens of thousands of demonstrators marched down a main road with traffic at a standstill.
They sang the protest movement's anthem and held up placards depicting the Chinese flag as a Nazi swastika.
Many of the protesters wore masks in defiance of a recently introduced ban on face coverings at public gatherings, and volunteers handed more out to the crowd.
Organizers said they wanted to use their right to protest as guaranteed by the city's constitution despite the risk of arrest.
The movement sprang out of opposition to a government proposal for an extradition bill that would have sent suspects to stand trial in mainland China, and then ballooned into broader demands for full democracy and an inquiry into alleged police brutality.